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COPYRIGHT DEPOSrr. 



COMSTOCK'S TECHNICAL SERIES. 



LIGHT, HEAT aisid POWER 
IN BUILDINGS 



BY 



ALTON D ADAMS, 

Member American Institute Electrical Engineers. 



^ 






New York 

WILLIAM T. COMSTOCK 

23 Warren Street 

1901 



THE l.iBRARY OF 

COMGSESS, 
Two CoHtSS Receiv£0 

DEC. m 1901 

COPVtJIGHT ENTRY 

CLASS ClxKXa No. 

-2.36 Z3 
COPY a. 




Copyright^ 

ALTON D. ADAMS, M. E. 

1901. 



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PREFACE. 

In this volume the object is to present in compact form 
the main facts on which selection of the sources for light, 
heat and power in buildings should be based. The problem 
for which a solution is sought is to determine the kind of 
equipment that will yield the service required in any case at 
the least total cost Such a purpose leaves little room for dis- 
cussions of theory relating to any particular class of apparatus, 
which has already been done in separate and larger volumes. 
It follows that the only novelty to be expected here is that of 
arrangement, by which the costs of service from widely dif- 
ferent sources are set down side by side. 

Should this arrangement prove convenient for those charged 
with the selection of apparatus for light, heac and power, the 
labor spent on the following pages will have accomplished 
its purpose. 

ALTON D. ADAMS. 



CONTENTS. 

Chapter I. — Cost of heat, light and power from public gas 
and electrical supply and from coal. Cost of light from 
gas and electrical supply. Cost of heat from gas and 
electrical supply. Cost of power from steam plant 
and from gas. Cost of power from electrical supply. 
Efficiency, heating effect and required labor with mo- 
tors and engines. Pages 9 — 13 

Chapter II. — ^Gas, electricity, steam and hot water in the 
distribution of heat, light and power. Gas as a means 
of illumination. Electricity for illumination. Dis- 
tribution of heat by gas. Distribution of heat by 
air, steam and hot water. Distribution of power by 
gas, electricity, belts and shafting and by steam. 
Conclusions 15 — 30 

Chapter III. — Advantages of the combined production of 
light, heat and power from steam. Light, heat and 
power from a single plant. Fuel required with boilers 
for light, heat and power. Heat from exhaust steam. 
Power and heating with given amount of steam. 
Heating and illumination with given amount of 
steam. Times of demand for light and heat 31 — 39 

Chapter IV. — Efficiency in production and distribution 
of heat, light and power from hot water and steam. 
Efficiency of heating by hot water. Efficiency of 
heating by steam. Combined efficiency of engines 
and boilers. Combined efficiency of boilers, 
engines, dynamos, wiring and electric motors. 
Combined efficiency of boilers engines, dy- 
namos, wiring and lamps. Combined efficiency ; 
from boilers to electric heaters 40 — 46 

Chapter V. — General requirements and safety of boilers. 
Explosive energy. Importance of safe and efficient 
boilers. Sources of danger in boilers. Conditions of 
safety in boilers 47 — 52 



8 CONTENTS. 

Chapter VI. — Boiler capacity. Measures of boiler capac- 
ity. Horse power of boilers. Heat required for feed 
water. Relations between heating and grate surfaces 
and the capacities of boilers. Rules to find heating 
surfaces of boilers. Water evaporated by each 
square foot of heating surface 53 — 69 

Chapter VII. — Combustion of fuels and boiler efficiency. 
Possible efficiency. Pounds of water evaporated. 
Sources of loss with boilers. Losses from wet fuel. 
Losses from imperfect combustion of carbon. Losses 
of volatile matter. Losses due to the temperature of 
chimney gases. Air required for combustion. Spe- 
cific heats of gases. Temperature resulting from 
the combustion of carbon. Heat passing to the boiler 
surfaces by radiation and from the gases of com- 
bustion. Heating power of semi-bituminous coal. 
Amount of air required for perfect combustion. In- 
itial temperature of combus-tion 70 — 86 

Chapter VIII. — Heating powers of fuels. How to deter- 
mine the heating power of fuel. Tests of anthracite 
coal. Tests of semi-bituminous coal. Tests of bitu- 
minous coal. Evaporation of water with the sev- 
eral kinds of coal. Chemical composition of anthra- 
cite coals. Chemical composition of different sizes 
of coal. Analyses of anthracite and semi-bitumi- 
nous coals. Analyses of bituminous coals. Effi- 
ciency with bituminous coals. Objections to the use 
of coal. Sources of coke and its value as fuel. Fuel 
value of illuminating gas compared with that of 
coal. Heating power of natural gas. Wood as fuel. 
Sources, weight and fuel value of charcoal. Peat as 
fuel. Heating power and value of petroleum for fuel. 

87—102 



Light, Heat and Power in Buildings. 



CHAPTER I. 



COSTS OF HEAT, LIGHT AND POWER FROM PUBLIC GAS AND 
ELECTRICAL SUPPLY AND FROM COAL. 

An open gas flame of sixteen candle power consumes 
five cubic feet of average gas per hour. At one dollar pe** 
i,ooo cubic feet, the cost of this gas flame is loo x .005 = 
0.5 cent hourly. Ten cents per kilowatt-hour is a 
moderate rate for electrical energy. Fifty-six watts is a 
fair rate of energy consumption for an incandescent lamp 
of sixteen candle power. Such a lamp requires an hourly 
expense of 10 x .056 = 0.56 cent at the rate for energy 
just named. Simple, non-condensing engines, with good 
boilers, will readily yield each horse-power hour of work 
with a consumption of four pounds of fairly good coal. 
If this coal costs three dollars per ton of 2,000 pounds, the 
expense for fuel per horse-power hour amounts to 300 x 
0.002 = 0.6 cent. This brake horse-power, when deliv- 
ered on the shaft of a dynamo which has an efficiency of 
90 per cent., produces an output of 746 x .90 = 671.4 
watts. At 56 watts each, the number of sixteen candle 
power lamps that may be supplied from this output is 
671.4 -f- 56 = 12. As the fuel cost of the horse-power 
hour is 0.6 cent, the charge against each sixteen candle 
power lamp is 0.6 --^ 12 = 0.05 cent hourly. 

Gas from public supplies usually contains 20 to 40 per 
cent, of the heating power of coal, from which it is de- 
rived, according to its variety. It seems at once evident 
from this fact that gas is ill-suited for general wanning 



10 LIGHT, HEAT AND POWER. 

in buildings, and when the cost of heat derived from gas 
at current pubHc rates is considered, its common use to 
heat buildings is seen to be entirely impracticable. As 
an illustration, take average city gas, yielding 650 heat 
units per cubic foot and selling for one dollar per 1,000 
cubic feet. This gas yields, therefore, 650 x 1,000 == 650,- 
000 heat units for one dollar on perfect combustion. Good 
anthracite coal has a heating power of 13,000 units per 
pound, or 13,000 x 2,000 = 26,000,000 heat units per ton. 
The amount of gas to supply heat equivalent to that from 
one ton of coal is therefore 26,000,000 -~ 650 = 40,000 
cubic feet, costing forty dollars at the rate named. Con- 
sidered as a general heating agent, electric energy is in 
a much worse position as to the portion of the energy of 
coal that it can deliver, and as to its cost at usual rates, 
than is gas. Ten cents per kilowatt-hour is a low average 
rate for electric energy, and as the kilowatt-hour is the 
equivalent of 3,412 heat units, this rate gives 34,120 units 
of heat for one dollar. To equal in heating power one ton 
of coal, the kilowatt-hours necessary are 26,000,000 -f- 
3,412 = 7,620, costing 7,620 X .10 == 760.00 dollars at the 
Tate named. In practice, the actual cost of electrical en- 
ergy at ten cents per kilowatt-hour, when used for gen- 
eral warming, is less than the cost of coal at 760 dollars 
per ton, because nearly all of the electrical energy is avail- 
able as heat in the apartments warmed, while more than 
75 per cent, of the total energy of coal is seldom so 
available. 

Mechanical power may be produced in buildings by 
means of either steam, gas or electrical energy. Power 
from steam implies both a boiler and engine. Gas de- 
velops power by means of an engine only, and electrical 
energy is transformed into mechanical work by a motor. 



LIGHT, HEAT AND POWER. 11 

For apparatus of equal quality, to develop a given power, 
the steam boiler and engine will usually cost most, the 
gas engine a somewhat less amount, and the electric 
motor least. The cost of either of these equipments for 
power production is very small compared with the fuel or 
■energy it consumes during its useful life, so that a moder- 
ate advantage in efficiency, or in the cost of power devel- 
opment, may more than offset a considerable excess in the 
first cost of the plant. 

It has been previously shown that a good steam plant 
should deliver a horse-power hour at a fuel cost of 0.6 
cent, when using fair coal at a price of three dollars per 
ton. Gas engines of small and moderate capacity, such as 
are commonly used in city buildings, may be fairly ex- 
pected to consume twenty cubic feet of gas per delivered 
horse-power hour. The gas impHed in this rating is of 
the quality generally distributed for illuminating purposes 
in towns and cities, having a heating power of not less 
than 650 units per cubic foot, on perfect combustion. If a 
gas of lower heating power is used, as one of the so- 
called fuel or producer gases, which may develop as little 
as 150 heat units per cubic foot, the consumption per unit 
of work will increase in inverse ratio to the energy of com- 
bustion. The lowest rate common for illuminating gas 
in the United States is one dollar per 1,000 cubic feet, 
and, while this rate is in force for but few cities, the cost 
of power may be stated for it as a convenient basis from 
which to compute the cost at other rates. At one dollar 
per 1,000 cubic feet, twenty feet of gas, to develop one 
brake horse-power hour, cost 100 x 0.20 = 2 cents. As 
coal to produce this same unit of work was found to cost 
0.6 cent, the fuel outlay for power from gas at one dollar 
per 1,000 cubic feet is more than three times as great as 



12 LIGHT, HEAT AND POWER. 

that for coal at three dollars per ton. Electrical energy 
for power production in motors can usually be had at 
materially lower rates than those charged when it is 
devoted to lighting purposes. A frequent rate for energy 
suppUed to electric motors is 3.33 cents per electrical 
horse-power hour, corresponding to a charge of loo dol- 
lars for a horse-power year of 3,000 working hours. Elec- 
tric motors do not, of course, deliver as mechanical work 
the equivalent of all of the electrical energy that they 
absorb, and the average efficiency, of small and medium 
sizes may be taken at 80 per cent., under the conditions of 
use. The exact figure for motor efficiencies increases 
slowly with the capacity of the motor. The average loss 
of 20 per cent, in motors raises the cost of their delivered 
work to 3.33 -^ .80 = 4.16 cents per horse-power hour. 
It thus appears that for the rates named the primary 
development of power in buildings with electric motors 
costs more than twice as much as that from gas and nearly 
seven times as much as that from coal, so far as the outlay 
for fuel and energy is concerned. In this comparison it 
should be noted that the steam is developed on the prem- 
ises, while the gas and electrical energy are procured from 
the public supply. Fuel or energy is obviously only one 
of the items that go to make up the cost of power in build- 
ings, and whether it is the most important should be de- 
cided on the circumstances of each case. Notwithstand- 
ing the low cost of fuel for the production of steam power, 
such power would be the most expensive possible where 
its total was small, no heating was required and it was 
necessary to employ an engineer for the care of the engine 
and boiler. For the case just named, where the power is 
quite small, and especially if it is fluctuating in amount 
and intermittent in point of time, electrical energy from 



LIGHT, HEAT AND POWER. 13 

the public supply would usually be the most economical 
source of power. Where heat is necessary in season to an 
amount nearly equal to or exceeding the capacity of the 
exhaust steam that would result from the desired power 
production, the steam plant is usually the most econom- 
ical primary source of power. In some other cases, where 
the necessary amount of heat is less than that which would 
be available from the exhaust of a steam engine of suffi- 
cient power capacity, a gas engine may be the means best 
suited for cheap primary power. This last is quite apt to 
be true where the use of power, though at a considerable 
rate, takes place during only a very few hours each day, 
or at times of day that are far apart. The gas engine is 
especially suited to the case just cited, because its waste 
heat is available for warming; it can be started at once 
without previous preparation, such as is necessary to get 
up steam in a boiler, and because the labor involved in its 
operation is less in amount and less exacting as to skill 
than that necessary on a steam plant. As an offset to the 
cost of energy for its operation, when employed as a pri- 
mary source of mechanical power, the electric motor re- 
quires only a trifling amount of attention, involving but a 
moderate degree of skill, and is ever ready for immediate 
use without previous preparation. The efficiency of the 
electric motor is six to ten times as great as that of steam 
or gas engines, and its wasted heat, that might be devoted 
to warming, is a very trifling matter. The primary source 
of mechanical power in city building is usually located in 
the basement, in a space especially devoted to it, and cer- 
tain features, such as heat, noise and vibration, that may 
belong to the apparatus are of minor importance com- 
pared with what they would have if it were located at 
various points through the building. For the great ma- 



14 LIGHT, HEAT AND POWER. 

jority of large city buildings that require mechanical 
power for a variety of purposes, such as electric lightings 
elevators and ventilation, as well as a large amount of heat 
for general warming, the steam plant is the most econom- 
ical source of power. 



CHAPTER 11. 

GAS, ELECTRICITY, STEAM AND HOT WATER IN THE DIS- 
TRIBUTION OF HEAT, LIGHT AND POWER. 

Gas and electrical energy are usually available for dis- 
tribution as lighting agents in modern buildings. The 
electrical energy is capable of ready production in build- 
ings and is also generally available from the pubHc supply. 
As illuminating gas cannot be readily produced in most 
buildings, it is open to the disadvantages of high cost. 
Three main disadvantages, aside from its cost, attach to 
the use of gas for illuminating purposes. These are its 
effect to heat and vitiate the air, the secondary quality of 
gas illumination, and the limits imposed on lamp arrange- 
ments, due to the presence of an open flame. If air is to 
be maintained at a fair standard of purity in a building, 
the use of gas for extensive illumination largely increases 
the volume of air to be handled per hour, because of the 
products of combustion given ofif. As is well known, the 
quality of ordinary gas light is decidedly inferior to arti- 
ficial illumination produced by some other means, both 
as to the sensation produced on the eye and the perma- 
nent effects on it of extensive use. In some cases of 
illumination, particularly where an artistic effect is de- 
sired, it is difficult or impossible to attain the result with 
gas, because of the flame and combustion. Electrical 
energy is almost an ideal source of illumination. Electric 
light is more pleasing to the human eye and less harmful 



16 LIGHT, HEAT AND POWER. 

on continued use than any other artificial illumination. 
As incandescent electric lamps involve no combustion 
whatever, and arc lamps only a trifling amount, their use 
adds nothing to the volume of air necessary to maintain 
any required standard of purity. Incandescent lamps, 
having their hot parts entirely enclosed in an air-tight 
globe, may be readily placed in any position or among 
any surroundings desired for artistic effects. Where it is 
necessary to place lamps so that they are difficult of ac- 
cess, the incandescent electric variety is particularly suit- 
able, because the Hght can be instantly produced or extin- 
guished without any electro-magnetic mechanism at each 
lamp, as is necessary for gas burners under such circum- 
stances. The wires required for the distribution of electric 
energy throughout a building occupy little more space 
than is required for gas pipes, and should be the subjects 
of scarcely more attention after they are properly in- 
stalled. Heat is distributed in buildings for two distinct 
classes of service, general warming and industrial pur- 
poses, such as cooking and the chemical and mechanical 
arts. For general warming the demand for heat extend- 
ing over a long period daily is fairly constant during such 
periods and its total amount is large, though very high 
temperatures at any particular point are not necessary. 
In the chemical and mechanical arts, and also frequently 
for cooking, the demand for heat is variable and intermit- 
tent, and its total amount is comparatively small. Indus- 
trial operations are very exacting, however, as to the de- 
gree of heat required at certain points, and temperatures 
must often be much above those necessary for general 
heating. A serious objection to the use of gas for general 
warming, in addition to its high cost, without the employ- 
ment of some agent, as air, water or steam, to distribute 



LIGHT. HEAT AND POWER. 17 

the heat, is that a fire must be maintained in every room. 
If gas is employed to heat air, water or steam at some 
suitable point, it ceases to be an agent of heat distribution 
in a building and can be considered only as a fuel. Air, 
water and steam are readily heated in suitable apparatus 
with any desired fuel, and the ease with which either may 
be distributed through a building renders each of them a 
good agent for general warming. Where hot water or 
steam are used for warming, their heat is derived directly 
from the gases of combustion and the radiation from the 
incandescent fuel. If air is to be the agent of heat dis- 
tribution, it is usually desirable and necessary, especially 
in large plants, to prevent contact of the air with the 
heated surfaces of boilers and furnaces, because their tem- 
peratures are so much greater than that desired for 
heated air that the quaHty of the air is injuri- 
ously affected. In most large plants, therefore, 
where air is the agent of heat distribution, it is 
heated by contact with coils that contain either 
hot water or steam. This water or steam is supplied 
from a boiler, and the loss incident to the second transfer 
of heat, or that from water or steam to air, is quite small 
in good apparatus. In the matters of first cost and re- 
quired space, the distribution of heat by hot air is at a 
disadvantage compared with that by some other means, 
especially where it is used exclusively. This disadvantage 
is due to the large volume of air necessary to supply the 
required heat and to the consequent sizes and arrange- 
ments of conduits for it. Where due provision must be 
made for ventilation, the primary disadvantages as to the 
size and cost of air conduits are largely offset by theif 
double service in the distribution of both heat and pure 
air. Probably the most economical arrangement, as to 



18 LIGHT, HEAT AND POWER. 

both first cost and that of subsequent operation, where 
both heating and ventilation are desired, includes con- 
duits of sufficient size to transmit the heated air necessary 
for ventilation and the necessary steam or hot water radia- 
tors to supply the remainder of the required heat. Steam 
possesses many advantages for the distribution of heat in 
buildings, and is probably more extensively used for that 
purpose in large plants than any other agent. The cost of 
pipes for steam heating in buildings and the room they 
require are moderate, but such a system is by no means 
ideal. One difficulty with steam distribution for general 
warming is the lack of heat regulation in the coils and 
radiators. Steam does all of its work as a heating agent 
at nearly constant temperature. Thus, steam at five 
pounds gauge pressure, or one that is seldom necessary to 
exceed in the heating system of a building, has a tempera- 
ture of 22.J degrees Fahr., while, after it has condensed 
to water at atmospheric pressure, thus yielding 970 
heat units per pound, the temperature is still 212 degrees. 
An inevitable result of the nearly constant temperature of 
steam heated surfaces is the waste of heat in mild weather, 
and more or less discomfort in over-heated apartments. 
Among the small disadvantages connected with a steam 
heating system are noises due to the collection of water in 
pipes and radiators, and an unpleasant odor of the steam 
that at times escapes through air valves on radiators. The 
system of heat distribution, by means of hot water circu- 
lating through the pipes and radiators, compares very 
faborably with steam heating in several particulars. The 
pipes for hot water heating, where the circulation of the 
water is maintained by the difference in temperature be- 
tween the water in the outflow or supply pipe and that in 
the return, are usually somewhat larger than steam pipes 



LIGHT, HEAT AND POWER. 19 

would be for an equal supply of heat. This excess in the 
size of hot water pipes over those for steam and equivalent 
service, adds only a moderate per cent, to their cost and 
still less to their required space Two of the most distinct 
advantages of the hot water heating system are its capacity 
for temperature regulation and to maintain a gradually 
diminishing supply of heat during some hours after the 
fire in the boiler furnace has been banked or gone out. 
While the temperature of steam is nearly constant at all 
of the pressures commonly employed in warming build- 
ings, the temperature of water in the low pressure system, 
or that open to the air, may be at any desired point below 
212 degrees. In mild weather, or when less than the max- 
imum rate of heat delivery is desired for general warming, 
a hot water system may be readily operated at any tem- 
perature that gives the heat supply desired. The capacity 
of water to store heat and then to give it ofif gradually 
renders it unnecessary to keep boiler fires In active opera- 
tion during the entire period of each day that heat Is 
necessary. Owing to the same property of water, the 
temperature of buildings heated with it does not fall as 
low during the daily period when fires are not In action, 
as is the case where steam is the heating agent. One 
result of the use of water instead of steam for heat dis- 
tribution Is that the daily hours of labor In the boiler room 
may be materially reduced. Reduction of the heat given 
off by a hot water system in mild weather, to the amount 
actually necessary to maintain the required temperature 
in a building, by lowering the temperature of the water 
and radiating surfaces, obviously tends to economy in 
fuel. The less the temperature of the heating surfaces of a 
boiler the larger is the amount of heat that is extracted 
from the gases of combustion. In steam heating above 



20 LIGHT, HEAT AND POWER. 

atmospheric pressure the temperature of at least a part of 
the boiler must be higher than 212 deg^rees at all times 
when any heat whatever is wanted. In hot water heating 
the temperature of the circulating water is varied to meet 
the demands for heat, being only 212 degrees at its highest 
point. It follows that the average temperature of boiler 
surfaces are materially lower in a hot water than in a 
steam heating system, and the gases of combustion may 
therefore be delivered to the flue with less of the fuel 
energy in them. This tends to high efficiency. Where a 
steam plant is used for the double purpose of heat and 
power, and the exhaust steam from engines is to be em- 
ployed in the heating system, the system of distribution 
by hot water presents some especial advantages. To cir- 
culate the exhaust steam through the pipes and radiating 
surfaces of a building, it is most common to operate the 
engines on two to five pounds back pressure. This back 
pressure reduces both the capacity and efificiency of 
engines, especially when they are of the compound type. 
There are certain special equipments on the market for 
use in connection with steam heating systems that make 
practicable the circulation of the steam at or below atmos- 
pheric pressure, but unless these equipments are used the 
back pressure in the case of engines has to be reckoned 
with. If, instead of circulating the steam from engines 
through the entire heating system of a building, it simply 
goes to a bank of coils for heating hot water, the back 
pressure on engines may be so reduced, without any 
special equipment, as to become a very small factor. Hot 
water may thus be raised to a temperature of 212 degrees, 
or that of a regular low-pressure hot water system. Cir- 
culation from these hot water coils through the heating 
system of a building takes place just as though the water 



LIGHT, HEAT AND POWER. 21 

was heated directly by the fire under a boiler. If it seems 
desirable in any case to reduce the sizes of pipes necessary 
for the hot water, where the circulation depends entirely 
on the difference in temperature in the outflow and 
return pipes, the hot water may pass through a 
pump that maintains any desired rate of circulation, 
through a heating system of any dimensions, and pipes of 
any size. If the average amount of exhaust steam avail- 
able is less than that required by the heating system, 
the small addition to the exhaust, resulting from the 
use of a pump, will usually be condensed in the heat- 
ing coils, so that the cost of pumping the hot water 
will be very slight. In this way the cost of pipes 
for a large system of hot water heating may be 
materially reduced below that of steam pipes for equiva- 
lent service. Another decided advantage of the system 
of hot water heating, in connection with a steam power 
plant, is the ability, by means of a hot water tank, to store 
the heat of exhaust steam, produced during one period of 
the day, for use at another. Some of the demands for 
power in large buildings are far from evenly distributed 
throughout the usual working hours of the day, and this 
is particularly true of the electric lighting load, which is 
mostly concentrated in three or four hours. Where ex- 
haust steam is distributed through the heating system oi 
a building, any excess above the amount that the system 
will condense during any particular period must be de- 
voted to some other purpose or wasted. With a system 
of hot water distribution, if the total heat of the daily 
product of exhaust steam does not exceed the total daily 
requirement for heat in the building for general warming, 
the surplus heat of the exhaust during any period of the 
day may be stored and subsequently utilized. Probably 



22 LIGHT, HEAT AND POWER. 

the best system for both heating and ventilation in a large 
building, where both first cost and the expense of opera- 
tion is considered, includes hot water and hot air, each 
circulated by mechanical means, under average circum- 
stances. In the distribution of heat for mechanical and 
other industrial purposes, considerations as to the supply 
of heat at just the right time and to the required degree 
are paramount, and the sum total of heat consumed is 
usually a secondary matter. The decided advantages of 
electrical energy and gas for heat production in many in- 
dustrial operations, owing to the effective control made 
possible wath them, of the time and degree of heat supply, 
often more than offset their high cost per unit of heat 
energy actually furnished. For some industrial purposes, 
where a nearly uniform and moderate degree of heat is re- 
quired in comparatively large amounts through consider- 
able periods, as in cooking and drying operations, hot 
water and steam are more available than gas and electrical 
energy, because of the low cost per unit of the heat they 
contain. The extended discussion of industrial applica- 
tions of heat is beyond the limits of the present work. 

Quite distinct from the question as to the most econ- 
omical source of the primary mechanical power in a build-, 
ing is that of the distribution of power to its several parts. 
While power may be developed with a steam plant in the 
basement of a building at a much less cost than that for 
which gas or electrical energy can be bought for equal re- 
sults, it frequently happens that the power is required in a 
number of small units throughout the building and very 
little of it can be applied to its ultimate use near the steam 
engine. A complete solution of the question of power pro- 
duction in modern buildngs must therefore include the 
means for its distribution to the points where it is wanted. 



LIGHT, HEAT AND POWER. 23 

There are four methods, either of which may be applied to 
power distribution in buildings, namely, mechanical 
equipment, such as belts and shafting, steam pipes to the 
several points where power is wanted, connected to en- 
gines there located, gas pipes running to suitably located 
gas engines, and electric circuits and motors. Distribu- 
tion by mechanical appliances or by steam pipes and en- 
gines is only possible, for most instances, when the pri- 
mary power plant is located in the building. Electrically 
distributed power may be had from either a local or a 
public plant. Gas pipes and engines must usually derive 
their supply from the public service mains. 

Power distribution by mechanical means involves the 
cost of belts, shafting and pulleys. For steam power dis- 
tribution, pipes and small engines must be provided. In 
like manner distribution by gas implies the necessary 
pipes and gas engines. If the energy is to be distributed 
electrically, wiring circuits and motors are necessary 
where the supply is taken from an outside source, and to 
these must be added an item for dynamos, when the pri- 
mary source of the power is in the building. Where the 
power of a local steam plant is to be distributed the first 
cost of engine, shafting and belting, of steam pipes and a 
number of small engines, and of engine, dynamo, wiring 
and motors for the same delivery of power at the points 
where it is desired, should be compared. The cost of 
steam pipes and small engines connected at points where 
the power is wanted will not differ greatly in many cases 
from the cost of one or more larger engines of equal ulti- 
mate capacity, and the belts and shafting necessary to dis- 
tribute the power. A large engine, dynamo, wiring and 
electric motors are quite sure, in most cases, to cost more 
than the same engine with the shafting and belting neces- 



24 LIGHT, HEAT AND POWER. 

saxy for distribution. To fairly decide between these 
three methods of distribution, the efficiency, convenience 
and the objectionable features of each should be consid- 
ered, as one or more of these items may much more than 
ofifset that of first cost. Where gas or electric energy 
from an outside source is to be distributed in a building 
for power purposes, gas pipes and engines must be paid 
for in one case and electric wiring and motors in the other. 
As a rule the gas pipes and engines will cost more than 
the electric circuits and motors. The costs of operation 
for the gas and electric equipments when supplied from 
the public mains has already been shown, and they in- 
clude the questions of efficiency. The main permanent 
objection to gas pipes for engines, over electric circuits for 
motors of equal capacity, is the, greater amount of room 
necessary to the former. Objections to gas engines are 
about the same as those to steam engines, and will be con- 
sidered when the latter are taken up. When the distribu- 
tion of power in a building from a local plant is considered 
the relative importance of the efficiency, convenience and 
objectionable features varies with the character of the 
building where the distribution takes place. In a factory 
building efficiency and convenience of operation, as they 
affect the cost of production, are of prime importance. 
For an office building, the absence of any very objection- 
able features is the most necessary requisite. Between 
these extreme classes of buildings there are a large num- 
ber where convenience of operation and objectionable 
features are of variable importance, but efficiency as to the 
consumption of fuel is highly desirable in almost every 
case. Where steam is distributed to the various parts of a 
building through long pipes for a number of small en- 
gines, two serious sources of loss are encountered. The 



LIGHT. HEAT AND POWER. 25 

long pipes are certain to condense considerable steam, 
and if they are not well insulated for heat the loss by con- 
densation rises to a large amount. Much more serious 
than the loss of heat from pipes with good insulation is 
that in the small engines themselves. While a large, 
simple engine should deliver a brake horse-power hour on 
not more than thirty pounds of dry steam, small engines 
of three to ten horse-power generally have a consumption 
of two to four times this rate. Including the losses from 
condensation in long pipes, it is probably safe to say that 
a considerable number of small engines, scattered over a 
large building and supplied from the main boilers, con- 
sume fully three times as much steam per unit of work as 
would one or more large, simple engines for the same 
aggregate power, when located near the boiler plant. If 
the conditions of service are such as to warrant the use of 
compound engines for large units, the equipment of 
numerous small engines would be at a still greater com- 
parative disadvantage. So low is the efficiency of numer- 
ous small engines at considerable distances from a boiler 
plant that the use of such equipments is mostly confined to 
a few cases where special conditions seem to warrant it. 
The power necessary to keep belts and shafting in motion 
varies, among other factors, with their extent, and is 
nearly constant whatever the power transmitted at any 
particular time. 

A system of shafting in first-class condition as to align- 
ment, and only moderate in extent, may have an efficiency 
as high as 75 per cent, when transmitting the maximum 
power for which it was designed, though 50 to 60 per cent, 
are much more common figures in actual work. As soon 
as the maximum rate of work slackens, the efficiency falls 
accordingly, being for the case cited about 50 per cent, at 



26 LIGHT, HBAT AND POWER. 

one-half, and zero at one-fourth the full engine load. 
Most of the power required in city buildings is decidedly 
intermittent in character, and nearly all classes of work 
partake of the fluctuating quality to a considerable extent. 
It follows that belts and shafting seldom work at their 
maximum capacity during any long period at a time, and 
often run with little or no load for some hours of each day. 
Where belts and shafting distribute power through a 
building of considerable size, it may be fairly said that the 
average all day efficiency of transmission is usually less 
than 40 per cent. This condition obviously leaves a large 
margin for improvement by some other method of dis- 
tribution. A part of this possible improvement is attained 
by the electrical method of power distribution. For elec- 
trical working the main engine or engines, instead of driv- 
ing by belt a system of extensive shafting, are coupled to 
one or more electric generators. These dynamos supply 
energy to electric circuits that extend to every part of the 
building where power is wanted, and are there connected 
to electric motors of suitable capacities. No such differ- 
ence exists between the efficiencies of large dynamos and 
of comparatively small motors, as was found to be the case 
between large and small steam engines. Thus at full 
loads the efficiencies of large dynamos of one hundred to 
several hundred horse-power capacity each should be 91 
to 93 per cent., while the efficiencies of motors from two 
to five horse-power capacity each should be 80 to 85 per 
cent. The efficiency of the electrical distribution is obvi- 
ously the combined efficiencies of the dynamos, lines and 
motors concerned. At full load the efficiencies of large 
dynamos may be taken at 92 per cent., electric circuits 96 
per cent, and motors 83 per cent., giving a figure of .92 x 
.96 X .83 = .816, or 81.6 per cent, for the combined effi- 



LIGHT. HEAT AND POWER. 27 

ciency of distribution. The efficiency of dynamos and 
motors drops with their loads, and a fair figure at one-half 
load for the machines just mentioned would be 88 per 
cent, for the dynamos and 'J2 per cent, for the motors. 
Loss in wiring, however, decreases with the square of the 
load, so that when the amperes flowing are reduced one- 
half the loss is cut down to one-quarter of its former 
amount, or to one-half the per cent, for the latter as for 
the former load. In the present instance, therefore, the 
line efficiency rises to 98 per cent, at one-half load. 

Combining the several values just given for the effici- 
ency of dynamos, motors and wiring at one-half load, it 
appears that the efficiency of the electrical distribution 
under this condition is 88 x .98 x .y2 = 62 per cent., 
nearly. These values for the efficiency of electrical dis- 
tribution at full and one-half load show an improvement 
over those for belts and shafting that corresponds to a 
large part of the theoretically possible saving. A satis- 
factory feature of the efficiency characteristics of the elec- 
trical equipment is that they remain nearly constant dur- 
ing the Hfe of the apparatus and are not subject to serious 
deterioration, as is the efficiency of belts and shafting, 
which suffers with changes in tightness and alignment. 

Further important contribution is made to the all day 
efficiency of electrical power distribution by the fact that 
all line and motor losses stop when the motors are shut 
down. Electrical power distribution in a building will 
often show an all day efficiency twice as great as that of 
belts and shafting. 

In buildings for factory and for some mercantile pur- 
poses, first cost and the subsequent efficiency of opera- 
tion are the points that determine the selection of the 
equipment for such power transmission as is required. 



28 LIGHT, HEAT AND POWER. 

Quite a different rule must be followed in buildings of the 
higher classes, where the tastes and convenience of ten- 
ants require the first consideration. Undesirable heat, the 
element of danger, noise and vibration must be eliminated 
to the largest practicable extent from methods of power 
transmission in most buildings for office, amusement, resi- 
dence and retail trade purposes. Belts and shafting obvi- 
ously include all of these objectionable elements, except 
that of heat, and also require a very considerable amount 
of room, so that they are rightly excluded from buildings 
in the classes just named. High pressure steam pipes and 
the small scattered engines which they may be used to 
supply involve an element of danger to persons and prop- 
erty because of the possible escape of steam. Their sur- 
faces at high temperature give off an amount of heat that 
may be very disagreeable in warm weather, and the noise 
and vibration incident to the reciprocating motions are not 
to be tolerated above the basement in a large number of 
instances. Gas engines and their supply pipes also in- 
clude an element of danger from the escape of gas, w^hile 
the escaping heat from the engine itself and the attendant 
noise and vibration are quite as objectionable as where 
steam is the motive power. In addition to the disadvan- 
tages just pointed out for small scattered engines supplied 
by steam or gas pipes, the labor cost in the operation of 
such engines is a comparatively large item. Electric 
power distribution in buildings remains to be considered 
as to the presence of the undesirable features just noted. 
As the pressure at which electrical energy is distributed in 
buildings is not usually great enough to cause injury to 
persons, the element of danger incident to the developed 
power is reduced to its lowest point. Electric motors 
have so hig^h an efficiency, usually 80 to 90 per cent., that 



LIGHT, HEAT AND POWER. 29 

the amount of waste heat they give off may be neglected 
for most practical purposes. The efficiency of electric 
wiring in buildings is even higher than that of motors, 
being usually above 95 per cent., so that such wiring 
has very little appreciable change in tempei-ature. 
The moving parts of electric motors differ materially 
from those of engines, in that the motions of 
the former are entirely rotary, while many of the 
latter are reciprocating. The noise and vibration that 
are almost always present with the operation of engines, 
apart from a solid foundation, are easily avoided with 
electric motors, in whatever part of a building they may 
be placed. In an electric motor there are only two sets of 
wearing surfaces, the bearings of the shaft and the com- 
mutator. All of the lubrication necessary for these sur- 
faces is automatic, and the motors operate hours and evefT 
days at a time without any necessary attention whatever 
beyond starting and stopping at the desired times. The 
absence of danger, objectionable heat, noise and vibra- 
tion with electric motors, together with the trifling amount 
of their required attention, make it practicable to dis- 
tribute electric power through all parts of the best classes 
of buildings, for elevators, ventilation and a variety of 
other purposes. 

The dependence of electric light, heat and mechanical 
power on the combustion of fuel has now been pointed 
out. The economic advantage of the production of these 
three forms of energy in a single plant has also been con- 
sidered. Efficiency and cost of operation, and also the 
facility of distribution in different ways in plants for light, 
heat and power in buildings has been discussed. Several 
general conclusions can be readily deduced from the fore- 
going matter. Buildings can be warmed by the combus- 



30 LIGHT, HEAT AND POWER. 

tion of coal in their local plants at fuel cost far 
below those incurred where heat is derived from 
the pubHc supply of gas or electric energy. If 
mechanical power is wanted in a building to an 
extent that does not require more steam during 
the cold months than would be necessary for heat- 
ing alone, both the power and heating may be had during 
these months with a small increase in the amount of fuel 
that would be consumed for heating. Only a small in- 
crease in the total steam and fuel consumed at a building 
during cold weather for heating is necessary if energy 
for electric light is taken from the same boilers. It fol- 
lows from the foregoing that the most economical means 
to supply light, heat and power in many large buildings is 
a local plant of steam boilers, engines and dynamos. This 
is especially true where the demands for each or all of 
these forms of energy are of long daily duration and large 
in amount. Where the requirement for heating is com- 
paratively small, and light or power are wanted in con- 
siderable amounts during short or intermittent daily 
periods, so that the labor of operation for a steam boiler 
bears an unusually large proportion to the total expense 
of plant operation, a gas engine may save enough labor to 
compensate for the increase of fuel expense over that for a 
steam boiler and engine. 



CHAPTER III. 

ADVANTAGES OF THE COMBINED PRODUCTION OF LIGHT, 
HEAT AND POWER FROM STEAM. 

Light, heat and power supplies in buildings are too 
often treated as independent problems, heat being de- 
rived from one source, light from another and mechanical 
power from a third. Another frequent practice is to com- 
bine the source of heat and power, and then derive light 
from an independent supply. Either of the plans just 
named is quite sure, under ordinary circumstances, to re- 
sult in more than the necessary cost. The best solution of 
the problem, where light, heat and power are required in 
a building, is to so combine equipment that all three are 
generated in the same plant or by the same fuel. The 
advantage of the combined plant lies in the fact that a 
moderate addition to the equipment required for heating 
and a slight increase in the fuel it consumes will usually 
suffice for the production of all the power and light de- 
sired in an office or mercantile building. Even where 
only heat and light are wanted it is usually much cheaper 
to make such additions as will produce light in connection 
with the heating plant than to derive the light from a 
public supply. To demonstrate these facts it is only 
necessary to consider the several equipments necessary 
for the production of light, heat and power and the pro- 
portions and relations between the amounts of energy 



32 LIGHT, HEAT AND POWER. 

consumed for each purpose, and then the charges for pub- 
lic supply. Heat is, of course, the almost exclusive 
source of light and power in buildings and coal the usual 
fuel. The usual agents of heat distribution in large build- 
ings are steam and hot water, also air heated by passing 
over steam coils. To supply steam or hot water, boilers 
are necessary, their capacity being about the same for 
either service. The steam coils for hot air also imply 
boilers. The only essential difference in the operation of a 
steam boiler for heating or power is that of gauge pres- 
sure. For steam heat alone the gauge pressure is usually 
not more than ten pounds, while for power with simplfe 
engines it may be anywhere from twenty to one hundred 
pounds by the gauge. The commonly accepted unit of 
heat is the amount required to raise the temperature of 
one pound of water from 39.1 to 40.1 degrees Fahrenheit, 
where water has its greatest density. The heat absorbed 
by one pound of water in passing through an increase of 
one degree in temperature at any point from 32 to 212 
degrees Fahrenheit is very nearly equal to the heat unit. 
To convert one pound of water at 40 degrees, the lowest 
temperature common for boiler feed to steam at 10.3 
pounds gauge pressure requires 1,147.1 heat units, while, 
if the pressure is raised to 100.3 pounds, the heat units 
absorbed by each pound of steam are only 1,177. I^ other 
words, to raise feed water at a temperature of 40 degrees 
to steam at 10.3 pounds pressure for heating, requires 
.974 of the heat and fuel that are required if the pressure 
is increased up to 100.3 pounds for power purposes. In a 
steam heating system the water of condensed steam is 
usually returned to the boilers at a temperature of about 
212 degrees, at which one pound of water contains 172.9 
units of heat above what it has at 40 degrees. As the 



LIGHT. HEAT AND POWER. 33 

water in a heating boiler is thus used over and over, the 
real expenditure of heat per pound of steam produced at 
10.3 pounds pressure is 974.2 units. In like manner, if the 
water of condensed steam used for power purposes at lOO 
pounds pressure is returned to boilers at the temperature 
of 212 degrees and thus repeatedly used, the heat absorbed 
by the steam per pound is 1,004.1 units, and the heat for 
one pound of steam at 10.3 pounds pressure is 97 per cent, 
of this amount. It is thus evident that the consumption 
of fuel to generate any given quantity of steam for power 
purposes in a simple engine is only about 3 per cent, more 
than the fuel necessary to produce an equal quantity of 
steam at low pressure for heating. If all of the steam 
used in engines was condensed during their operation, the 
facts just cited would have little bearing "on the economic 
use of the same boilers for both heating and power; but 
the smaller part of the steam entering engines is con- 
densed therein. The temperature limits in engine cyHn- 
ders are such that only a fraction of the heat in the steam 
entering them can be extracted for power production and 
the remainder escapes as exhaust steam and water. The 
proportion of steam and water leaving an engine cylinder 
is the main factor to determine the heat that may be used 
for other purposes. If the engine exhausts at atmospheric 
pressure, the temperature of both the water and the steam 
on leaving the cylinder is 212 degrees, as this is the high- 
est temperature that either can have at that pressure. 
Each pound of water in the engine exhaust contains only 
172.9 heat units above water at a temperature of 40 de- 
grees, but each pound of steam contains 1,138.6 heat units, 
or 965.7 more than one pound of the water, this being the 
latent heat of steam, or the amount of heat necessary to 
change one pound of water at the temperature of 212 



34 LIGHT, HEAT AND POWER. 

degrees to steam of that temperature at atmospheric pres- 
sure. If it is desired to utilize the exhaust §team of en- 
gines in a heating system, it will frequently be necessary 
to let the engines exhaust at a pressure a little above that 
of the air to give the required flow of steam in the heating 
pipes, but this back pressure on the engines, as it is called, 
is seldom more than five pounds. As the total contained 
heat of steam above water at 40 degrees is 1,138.6 heat 
units at atmospheric pressure, and only 1,143 heat units at 
five pounds above the atmosphere, and as the water of 
condensed steam may be expected to cool to 212 degrees 
before it leaves the heating pipes, the heating power of 
steam may be considered the same as at atmospheric 
pressure within these limits. The weight of exhaust 
steam and water leaving an engine cylinder must equal 
the weight of steam entering it from the boilers. Water 
and steam make up the engine exhaust in varying propor- 
tions that depend on several factors, but a fair relation for 
single cylinder engines is 80 per cent, steam and 20 per 
cent, water. As 1,004 heat units must be added to one 
pound of water at 212 degrees to produce one pound of 
steam at 100.3 pounds gauge pressure, and this steam, 
when it is reduced to about five pounds pressure at the 
engine exhaust, can yield 965.7 units to a heating system, 
one pound of exhaust steam has 96 per cent, of the heat- 
ing power of the same weight at 100.3 pounds pressure. 
But as only 80 per cent, of engine exhaust is steam, the 
actual heating power of the exhaust, compared with the 
heat imparted to water at 212 degrees to generate steam 
at 100.3 pounds pressure, is 76.9 per cent. That is, the 
use of steam in simple engines absorbs only about 23 per 
cent, of the heat required to produce it from water at 212 
degrees. Applying this per cent, to the latent heat of 



WGHT, HEAT AND POWER. 35 

Steam at air pressure — that is, 965.7 units — shows that for 
each pound of steam suppHed to the engines 772.5 units 
of heat may be extracted from the exhaust before it be- 
comes water at 212 degrees temperature. To obtain 965.7 
heat units from a boiler devoted exclusively to warming, 
requires the addition of only that amount per pound to 
water at 212 degrees, since it is considered that all the 
water of condensed steam returns to the boiler at that tem- 
perature. In order 'to derive 965.7 'heat units from exhaust 
steam, however, on the above basis, the heat that must be 
added to water at 212 degrees is found from a division of 
the 965.7 by 76.9, which shows the amount to be 1,255 
units, or an increase of 30 per cent, over the heat neces- 
sary in a boiler used only for warming. If, therefore, the 
entire steam supply from a boiler is to be used for power 
in simple engines and the exhaust applied to heating, 30 
per cent, more fuel will be necessary than that required 
for the heating alone. 

It is next in order to determine the amounts of power 
and heating that may be done with the same steam. In 
simple engines of moderate capacity, subject to some 
variation of loads, it is fair to put the steam consumption 
at 30 pounds per brake horse-power hour. As found 
above, 772.5 units of heat may be derived from each 
pound of steam entering the engines for the heating sys- 
tem by utilizing the exhaust steam. At the; rate of 30 
pounds of steam per horse-power hour, the ex^haust may 
supply 23,175 heat units for warming purposes hourly for 
each horse-power delivered by the engines. Other factors 
remaining constant, the rate at which heat is given ofif by 
radiating surface depends on the difference between its 
temperature and that of the surrounding air. An average 
value for the hourly em.ission of heat from radiating sur- 



86 LIGHT. HEAT ANB POWER. 

faces is 1.75 units per square foot for each degree by 
which its temperature exceeds that of the surrounding 
air. With radiating surfaces at 212 degrees and the sur- 
rounding air at 70, the difference is 142 degrees, and the 
heat given off by each square foot of radiation, on the 
basis of 1.75 units per degree of difference, is 248.5 heat 
units per hour. As each horse-power hour was found to 
yield exhaust steam containing 23,175 latent heat units, it 
is able to supply 93 square feet of the radiating surface just 
considered. If 3.5 heat units are required for each cubic 
foot of heated space per hour, a rate that is usually ample 
for warming offices and stores, 71 cubic feet may be 
heated by each square foot of radiating surface and 6,603 
cubic feet per horse-power of engine delivery. By an in- 
crease of 30 per cent, in the fuel necessary to supply 93 
square feet of radiating surface in a simple heating plant, 
one brake horse-power may be delivered by a simple 
engine, in addition to the maintenance of the radiating 
surface, as before. 

Having noted the relation between the work of engines 
and the heating capacity of their exhaust steam, it remains 
to determine the illumination that the power correspond- 
ing to any heating effect can produce. One brake horse- 
power at the engine shaft, delivered to a good dynamo at 
90 per cent, average efficiency, produces an output of 
671.4 watt of electrical energy, since 746 watts are the 
equivalent of one mechanical horse-power. At a con- 
sumption of 3.5 watts per candle-power, a rate now regu- 
larly attained with incandescent lamps, the 671.4 watts 
maintain 21 1.3 candle-power of electric illumination. This 
illumination may be had in lamps ranging from ten to 
several hundred candle-power each, as desired. If the 
usual lamp of sixteen candles is selected, consuming 56 



LIGHT, HEAT AND POWER. 87 

watts, twelve may be operated for each horse-power de- 
livered to the dynamos. It thus appears that 30 pounds 
of steam, entering the simple engine, supplies one brake 
horse-power hour, the exhaust 93 square feet of radiation, 
and, if the power is applied to a dynamo, operates twelve 
incandescent lamps of sixteen candle-power each during 
one hour. The fuel cost of the brake horse-power hour, 
or for the incandescent lamps, is obviously only the in- 
crease over that necessary for each 93 square feet of 
radiation hourly when this is supplied directly from 
the boiler, provided that at least this much radiat- 
ing surface is necessary. To determine the money 
cost of the 30 per cent, increase in the heat re- 
quired of boilers where power as well as heating 
surface of a given amount is to be supplied, the effi- 
ciency of boilers must be considered. Good boilers of 
moderate capacity, as commonly used in large buildings, 
should evaporate as much as 7.5 pounds of water at 212 
degrees to steam at 100 pounds pressure per pound of 
coal burned, and many are doing much better than this. 
On this basis, four pounds of coal must be burned to 
supply 30 pounds of steam to an engine for the delivery of 
one brake horse-power hour. At a price of $3 per ton, 
these four pounds of coal cost .6 cent. It has already been 
shown that the steam for the engine absorbs from the 
boiler 1.3 times the heat that is taken by steam used only 
in the radiators that the exhaust for each horse-power of 
engine output will supply. In other words, y^j per cent, 
of the heat absorbed by the steam for engines is applied 
by means of the exhaust to the heating surface, and would 
be required for this surface if the engine was not in use. 
The .6 cent expended to supply steam to an engine for 
one horse-power hour should therefore be charged .'jy or 



SS' LIGHT, HEAT AND POWER. 

.462 cent to heating and .138 cent to power production. 
If this one horse-power is applied to the production of 
electric light in twelve incandescent lamps of sixteen 
candle-power each, the fuel cost per lamp hour is o.oii 
cent. It may be questioned whether all of the exhaust 
steam from engines used to operate dynamos for electric 
light can be utilized during the heating season, and a few 
figures will give some information on the subject. The 
space that can be heated by the exhaust steam per brake 
horse-power of engines in operation has been shown to 
be 6,603 cubic feet. A room 10 feet from floor to ceiUng, 
and with a floor space of 20 feet by 33, contains 6,600 
cubic feet. The floor of this room includes 660 square 
feet, and if one sixteen candle-power lamp is allowed for 
each 55 square feet the room will have twelve of these 
lamps. As twelve of the sixteen candle-power lamps are 
maintained per horse-power delivered to a dynamo, and 
the exhaust steam per horse-power heats the room in 
question, it seems that the dynamos operated by simple 
engines will supply energy to illuminate the space that the 
exhaust steam will heat. The illumination here assumed 
is about the average, while the space warmed per unit of 
heat represents frequent practice. It should also be noted 
that the comparison just made is based on the simul- 
taneous use of both light and heat. The facts are that in 
the heating season lamps are in use only one-half to one- 
fourth of the hours per day that steam is required in the 
radiators. These facts still further increase the space that 
may be lighted over that which may be heated from the 
energy of steam used by dynamo engines. The lack of 
coincidence in point of time during each twenty-four 
hours in the demands for light and heat in buildings is an 
obstacle to the economic application of steam to heating 



LIGHT, HEAT AND POWER. 39 

and the production of electric energy. The demand for 
heat is greatest during the morning hours, but continues 
in a large degree throughout the day. Much the greater 
part of electric lighting, on the contrary, is crowded into 
the late afternoon and evening. As a result, the supply 
of exhaust steam, while entirely inadequate for heating 
purposes during the first half of the day, is much greater 
than can be immediately utiHzed during some hours in 
the second half. There are means at hand, however, by 
which either heat or electric energy not wanted at the 
time of its production may be stored and applied during 
a subsequent period. 



CHAPTER IV. 

EFFICIENCY IN PRODUCTION AND DISTRIBUTION OF HEAT, 
LIGHT AND POWER FROM HOT WATER AND STEAM. 

When a boiler has transferred a portion of the heat 
resuhing from combustion of fuel to its contained water 
and steam, the first step toward the production of light, 
heat or power at the points where it is desired has been 
taken. Escape of heat which does no useful work frorn 
the furnace and boiler is only the first of a series of losses 
that intervene between the latent energy of the fuel and 
the desired effects. Heat imparted to the contents of the 
boiler may be desired for consumption in that form of 
energy, or this heat may be transformed to power or light, 
as required. If the water or steam of the boiler are de- 
voted to heating purposes, a large share of the contained 
energy may become available at the point of final use, but 
where power or light is the ultimate object the possible 
per cent, of energy that may appear as useful effect is 
much smaller. Heat from a boiler may be distributed 
for general warming by either hot water or steam. If the 
water is heated under open-air pressure and to a tem- 
perature of about 212 degrees, nearly i8i heat units must 
be added to each pound of water when its initial tempera- 
ture is 32 degrees Fahrenheit. Only a fraction of this 
temperature can be taken from the water by radiators 
under ordinary conditions, because the cost of radiators 



LIGHT. HEAT AND POWER. 41 

and their required space become too great unless a high 
average temperature is maintained. Allowing for an 
ordinary case a fall of 40 degrees for the temperature of 
water while in radiators, it appears that water entering 
boilers at 32 degrees and leaving them at 212 will have 
22.1 per cent, of its added heat extracted by radiators, if 
only its first round of circulation is considered. This 
result presumes no loss of heat from the pipes that 
conduct the water to and from the radiators. Such an 
escape of heat may be a loss if the pipes are in a space 
where heat is not wanted, or may be treated the same as 
heat from the radiators if the pipes are in heated space. 
When water returns to boilers from its first round 
through the radiators enough heat to compensate for the 
lost temperature must be added. Disregarding, then, 
any loss from pipes, the efficiency of hot water 
distribution in the present case is 22.1 per cent, 
for the first round of circulation. In each subse- 
quent round of circulation the water yields for use- 
ful effect all of the heat corresponding to the 40 degrees 
of temperature last added by the boiler, and the efficiency 
is 100 per cent. Where a hot-water heating system is in 
active operation during a large number of hours per day, 
the amount of heat necessary to raise the volume of cir- 
culating water from its initial outside temperature to 212 
degrees is trifling compared with the total heat subse- 
quently imparted to the water. Consequently, the effi- 
ciency of the heating system beyond the boiler may be 
nearly 100 per cent. A small loss should be allowed to 
cover leakage and evaporation from the pressure tank, s6^ 
that where there is no waste radiation from pipes, and the 
period of active operations extends through the larger 
part of each day, distribution efficiency may be fairly 



42 LIGHT, HEAT AND POWER. 

taken at 95 per cent. Presuming boilers to transfer to 
their contained water 70 per. cent, of the total energy of 
fuel consumed, the useful heat derived from hot water 
may represent .95 x 70 = 66.5 per cent, of the possible 
heat from the combustion of coal. In steam heating at 
air pressure, with water having an outside temperature 
of 32 degrees, nearly 181 heat units must be added to 
each pound of water, as before, and in addition to this 966 
heat units will be absorbed by each pound when it is con- 
verted into steam, making a total of 1,146 units per 
pound. Presuming, as before, that the heat escaping from 
pipes is as useful as that from radiators, the steam heating 
system may deliver for useful efifect 966 -~ 1,146 = 84.3 
per cent, of the heat imparted to the contents of the boiler, 
considering only the first production and condensation of 
steam. The same per cent, of efficiency applies constantly 
to cases where the condensation from radiators is lost 
and does not return to the boilers. If all of the condensed 
steam is returned to the boilers, the distribution system 
may have an efficiency of 100 per cent., after the boiler 
water has once been raised to a temperature of 212 de- 
grees. Some of the steam in pipes and radiators is quite 
sure to escape through small leaks and at the air valves, 
so that an efficiency of 100 per cent, is not reached for 
the heating effect of steam sent into the pipes from water 
at 212 degrees. 

It may be fairly assumed, however, that the leakage of 
steam will not amount to more than 5 per cent, with good 
pipes and radiators. Where a steam heating system is in 
active use during the larger part of each day, the amount 
■of heat necessary to bring the water required to fill the 
boilers once to the boiling point is a trifling part o£ the 
total. For the case of water from radiators returned to 



LIOHT, HEAT AND POWER. 43 

boilers and used over and over, a steam heating system, 
with a boiler of 70 per cent, efficiency, may be expected 
to deliver for useful effect 70 x .95 == 66.5 of the possible 
heat from combustion. From this it appears that for the 
conditions named the efficiency of steam and hot water 
heating systems are substantially equal. 

Where steam is devoted to power production, the por- 
tion of its contained energy that may be recovered as 
mechanical work is limited by the initial and final tem- 
peratures of the steam entering engine cylinders. For the 
most ordinary conditions in the power plants of 
buildings, steam is supplied to simple engines at 
about 100 pounds gauge pressure and is exhausted 
into open air. Each pound of this steam contains 
1,185 heat units above water at 32 degrees Fahrenheit, 
and as much as 30 pounds are generally consumed per 
delivered horse-power hour with simple engines. The 
heat passing into the engine per horse-power developed is 
thus 1,185 X 30 == 35^550 units per hour. One horse- 
power hour is the equivalent of 2,545 heat units, so that 
an engine as above has an efficiency of 2,545 -7- 35>55o =^ 
7.1 per cent. 

With boilers that deliver in steam 70 per cent, of the 
total energy of the fuel consumed, the combined efficiency 
of the plant is .70.x 7.1 = 4.9^ per cent. If the exhaust 
steam is used to heat the boiler feed water from a tem- 
perature of 32 to 212 degrees, 181 heat units are thereby 
saved per pound, or 181 x 30 = 5,430 units per horse- 
power hour. Deducting this amount of heat from the 
charge previously made against the engine, leaves 35,550 
— 5,430 = 30,120 heat units as the consumption of heat 
per horse-power hour. Dividing the heat equivalent of 
one horse-power hour by the last named quantity, shows 



44 LIGHT, HEAT AND POWER. 

the efficiency of the engine to be 2,545 -f- 30,120 = 8.4 
pel* cent. Using again the number 0.70 to represent 
boiler efficiency, the boiler and engine combined yield in 
the form of mechanical energy 8.4 x .70 == 5.8 per cent, of 
the total heat of combustion. This number is in marked 
contrast with the efficiency of 66.5 per cent, found for 
both hot water and steam heating systems. The frequent 
practice by which exhaust steam is employed for heating 
purposes rests on the fact that a pound of steam from 
the engine is as good in the radiators as is a pound 
from the boilers. Steam at 100 pounds gauge pressure 
contains 1,185 heat units per pound above water at 32 
degrees temperature. At open-air pressure this same 
steam still contains 1,146 heat units per pound, showing 
a loss of only 3.3 per cent, of its contained heat. 

In many buildings power developed by steam is desired 
for use in small quantities at a considerable number of 
points, and dynamos, wiring and electric motors are the 
most suitable means of distribution. For this case the 
losses at the boilers and engines are further increased by 
others in the electrical equipment. Average efficiencies 
for dynamos, wiring and electric motors may be fairly 
taken at 90, 98 and 80 per cent., respectively. The com- 
bined efficiency of these three electrical elements is, there- 
fore, 90 X .98 X .80 = 70.5 per cent. For the case of a 
boiler and simple engine, the combined efficiency was 
found to be 5.8 per cent., when feed water is sent to the 
boiler at a temperature of 212 degrees. Combining this 
figure for efficiency with that just found for the electrical 
system from dynamo shaft to motor shaft, it appears that 
the motor will deliver in mechanical work 5.8 x 0.705 = 
4.1 per cent, of the energy that complete combustion of 
the fuel will yield. It should be noted here that the elec- 



LIOHT. HEAT AND POWER. 45 

trical .equipment is far more efficient than the steam power 
plant. While the steam plant named is able to deliver 
only about 5.8 per cent, of the total fuel energy as 
mechanical work, the electrical system of dynamos, wir- 
ing and motors yields at the motor shaft more than twelve 
times this per cent, of the work done on the dynam5 
pulley. 

Where steam power is devoted to electric lighting, only 
dynamos and wiring intervene between the engines and 
lamps, and the combined efficiency of these two electrical 
elements is 90 x .98 = 88.2 per cent. With the same 
efficiency as before for the engine and boiler, the electric 
lamps receive 5.8 x .882 ^d::i 5.1 per cent, of the energy 
that may be developed by the fuel consumed. In the 
lamp, whether arc or incandescent, is seen the one ele- 
ment of an electrical system that is highly inefficient. 
While the dynamo delivers as electrical energy 90 or 
more per cent, of the work done on it by the steam en- 
gine, electric lamps emit as light less than 2 per cent, of 
the energy entering them. Comparatively, however, elec- 
tric lamps are highly efficient, since they yield as light a 
much higher per cent, of the applied energy than does the 
tallow dip, the oil burner or the gas jet. 

Electric heaters for general warming have an efficiency 
of 100 per cent.; that is, they transform into useful heat 
all of the electrical energy sent into them. 

As the efficiency of dynamos is 90 or more per cent., 
the combined efficiency of the dynamo and electric heatei 
is at least this figure for ordinary cases. With a loss of 2 
per cent, in wiring between the dynamo and heater, the 
latter radiates as heat the equivalent of 90 x .98 = 88.2 
per cent, of the mechanical energy expended to drive the 
dynamo. If the greater part of fuel energy could be 



46 LIGHT. HEAT AND POWER. 

made available as mechanical work at the dynamo, elec~ 
trie heaters would quickly replace every other form, be- 
cause of their efficiency, each of regulation and the low 
cost at which they can be made. As matters stand, how- 
ever, general warming of buildings by electric heaters is 
impracticable because of the great amount of fuel neces- 
sary. This may be seen from the fact that with the above 
steam plant only 5.8 x .882 = 5.1 per cent, of the heat of 
coal is radiated by the electric heater. 



CHAPTER V. 

GENERAL REQUIREMENTS AND SAFETY OF BOILERS— EX- 
PLOSIVE ENERGY. 

As the several forms of energy required in buildings all 
depend ultimately on steam or hot water for their produc- 
tion, in most cases, boilers may be considered of prime 
importance in the development of light, heat and power. 
Safe and efficient boilers do not necessarily imply a satis- 
factory and efficient power plant, but it is safe to say that 
such a plant cannot be had without these qualities in the 
boilers. The office of a steam or hot water boiler is ob- 
viously to transfer the heat resulting from the combustion 
of fuel to its contained fluids. That portion of the 
total heat of perfect combustion that appears in the hot 
water and steam is a measure of the boiler efficiency. 
Safety with a boiler depends not only on the strength of 
its parts in proportion to the strains which they must 
ordinarily undergo, and on the attachments that tend to 
prevent accidents, but also on the power of the boiler to 
do damage under any combination of circumstances. 
Satisfactory operation of a boiler may depend quite as 
much on the conditions under which it is placed as on its 
inherent good qualities. Where fuel is very expensive 
the first cost of boilers is of small moment compared with 
their efficiency, but when fuel is very cheap a gain of 
efficiency may be more than offset by increased interest 
and depreciation charges on the investment. 



48 LIGHT, HEAT AND POWER. 

In general, a boiler should be selected according to the 
degree of safety required at the point of use, the cost of 
fuel, the quality of the water and the shape of the space for 
which it is intended. 

The dangers from boilers are due to the fact that they 
are great reservoirs of energy. This energy exists in the 
boiler as heat, but is transformed into motion when a 
break allows the boiler's contents to escape. An excess 
of pressure in a boiler above what it is able to resist causes 
a break, but this excess of pressure is not the destructive 
force of the explosion, but simply gives that force a 
chance to act. Where a break in a boiler occurs the heat 
in its escaping water changes to mechanical energy 
through expansion of the water into steam, and this ex- 
pansion operates to project the boiler or its parts with 
great force and high velocity. 

The steam in a boiler is sometimes spoken of as the 
destructive agent in case of an explosion, but it is really 
the steam formed after a boiler bursts that does the dam- 
age. The energy in the steam of a working boiler under 
normal conditions — that is, one-half to three-fourths full 
of water — is small in amount compared to the energy in 
its water. For example, take a boiler two-thirds full of 
water and working at 125 pounds gauge pressure. Each 
cubic foot of dry steam in this boiler contains 351 heat 
units more than an equivalent weight of water; that is, .31 
pounds at 212 degrees. Each cubic foot of water in this 
boiler, if at the temperature of 352 degrees, to corre- 
spond with the steam pressure of 125 pounds gauge, con- 
tains about 7,920 units of heat above an equal weight of 
water, or 55 pounds, at the temperature of 212 degrees. 
The temperature of 212 degrees is taken as the point from 



LIGHT, ilEAf AND POWER. 49 

which to compute the energy of both the water and steam, 
because water flashes into steam under atmospheric pres- 
sure at 212 degrees or any higher temperature. Of course, 
only a Httle of a body of water at just 212 degrees can 
change to steam when separated from its source of heat 
and exposed to the open air, because 966 heat units are 
absorbed by each pound of steam then formed, and this 
heat must be taken from and lower the temperature of the 
body of water. The higher the temperature of a body 
of water above 212 degrees when exposed to the open 
air the larger the part of the water that changes to steam. 
From the above figures it appears that each cubic foot of 
water in a boiler working at 125 pounds gauge pressure 
contains 7,920 -f- 351= 22.2 times as much heat energy 
above water at 212 degrees as each cubic foot of steam ifl 
the same boiler. If the boiler contains two cubic feet of 
water to one of steam, the ratio of the energy that the 
water may liberate when exposed to the air to the energy 
of the steam is 22.2 x 2 == 44.4 to I. In the case of a 
boiler explosion the mechanical work done in huding the 
parts of the boiler is thus mostly derived from the expan- 
sion of the steam formed from the liberated water. If the 
water remained in the boiler under normal conditions of 
operation its contained heat energy would be gradually 
imparted to the steam during a comparatively long period 
of time, but when a very large rent in the boiler allows its 
contents to escape in a few seconds the stored energy of 
the water is converted into work in so short a time that a 
very great force is exerted on surrounding materials. 
When the destructive effects of boiler breaks or explo- 
sions are to be considered, it is thus evident that the quan- 
tity of water that may escape and the element of time are 
of the highest importance. 



50 LIGHT, HEAT AND IJI^WER. 

The difference between a bad leak in a boiler that may 
never be heard of outside the fire room and an explosion 
that lands the boiler plates half a mile from their founda- 
tion is simply one of time during which the contents of 
the boiler escape. Different boilers of the same working 
capacity vary much as to the amount of contained water 
in each, and also as to the rapidity with which this water 
can escape by a rupture of some of the parts. 

Where the highest degree of safety from explosions is 
desired it is obvious that, other things being equal, boil- 
ers should be selected that contain only a small amount of 
water relative to their capacity, and are of such propor- 
tions and construction that their contents will be much 
retarded in its escape if a break occurs. An ex- 
cess of internal pressure above what the boiler 
will withstand is the general direct cause that pro- 
duces rupture of the parts and the subsequent explosions. 
This rupture of boiler tubes or plates is usually brought 
about by their deterioration with rust, their overheating, 
or else by a large increase of the internal pressure above 
that for which the boiler was designed. To guard against 
these dangerous conditions in a boiler its strength should 
be ample for the intended pressure, its design should 
be adapted to the kind of water that must be used, the 
internal as well as the external surfaces should be capable 
of ready inspection and cleaning, the safety valve should 
be of a type that is not easily put out of the proper ad- 
justment, either by intent or accident, and the 
surfaces most exposed to the heat should be 
protected by one or more fusible plugs. Water that 
must be used in boilers, in many places, contains quite an 
amount of mineral matter, which is deposited on the 
interior surfaces of boilers as steam is formed. Such de- 



LIGHT, HEAT AND POWER. 51 

posits of mineral matter or scale are very poor conductors 
of heat, so that the metal of the boiler plates or tubes, 
where they are attached, instead of remaining at about the 
temperature of the contained water, may be raised much 
above that point. As the temperature of iron or steel rises 
much above that of the water in high pressure boilers it 
grows materially weaker. It therefore happens that boiler 
plates and tubes, ample in strength to withstand the pres- 
sure for which a boiler is rated, when they are at or near 
the temperature of the contained water, often fail under 
the normal pressure because, having been coated with a 
thick layer of scale, they are overheated and lose their 
ordinary strength. Rust frequently attacks some parts of 
boilers more than others, and if the extent of its inroads 
on all interior surfaces cannot be determined and its 
progress stayed, points may be developed in a boiler 
where the strength is far below the necessary standard of 
safety. It is easy to conclude from these facts that all 
interior surfaces of boilers should be easy of inspection 
and capable of being cleaned. It also follows that where 
mineral deposits are likely to occur a boiler should have 
as few surfaces as possible where such scale may rest ex- 
posed to the flames. As a general rule, these adverse con- 
ditions as to scale and rust may be avoided by require- 
ments that only straight tubes, in nearly vertical positions, 
and plates similarly placed, be exposed to the furnace 
flames, and that enough room be left between all interior 
surfaces for full inspection. Safety valves which are in- 
tended to limit the possible pressure in a boiler to the 
normal rating of its parts by an escape of steam when the 
rated pressure is exceeded may fail through either intent 
or accident to perform their function. The valve con- 
struction should be such that no rusting of its parts can 



52 LIGHT. HEAT AND POWER. 

tend to prevent the opening of the valve on an excess of 
pressure. A valve should not be of a type where the limit- 
ing pressure can be raised by simply shifting the position 
of a weight on a lever arm or tightening a spring. Prob- 
ably the safest valve is one direct weighted in plain sight. 



CHAPTER VI. 

BOILER CAPACITY. 

Boiler capacity is measured by the amount of heat that 
may be transferred to the contained water and steam per 
unit of time, under given conditions as to fuel, firing and 
draught. A convenient measure of the heating effect in a 
steam boiler is the evaporation of one pound of water at 
212 degrees to steam of the same temperature under 
atmospheric pressure. One pound of water then evapo- 
rated absorbs 965.7 heat units. Where boilers are used 
for hot water heating it may be more convenient to meas- 
ure capacity by the product of the pounds of water heated 
by the temperature through which it is raised in degrees 
Fahrenheit per unit of time. The unit of heat is the 
amount necessary to raise one pound of water one degree 
from the temperature of 39.1 degrees Fahrenheit. The 
heat absorbed by one pound of water when raised one 
degree in temperature at any point between 32 and 212 
degrees is very nearly the same as the exact unit of heat, 
and may be treated as the heat unit in ordinary calcula- 
tions. It follows that the product of the weight of water 
in pounds heated by a boiler per unit of time by the de- 
grees through which the temperature of the water is 
raised gives the output of the boiler in heat units for that 
time. A boiler that raises 966 pounds of water one degree 
in temperature per unit of time thus has a capacity equal 



54 LIGHT, KEAT AND POWER. 

to that of a boiler that evaporates one pound of water 
from and at 212 degrees under atmospheric pressure dur- 
ing the same period, all other conditions remaining con- 
stant. Simple as it thus is to state the capacity of boilers, 
whether for steam or hot water, in definite units, a less 
accurate and somewhat misleading rating is often used. 
It has long been customary to specify boilers as of so 
many horse-power, but it should be noted that one horse- 
power effect in a boiler is an entirely different thing from 
one horse-power with an engine. When delivering one 
horse-power an engine raises 33,000 pounds one foot high 
each minute, or overcomes any other resistance through 
any other distance, so that the product of the resistance 
in pounds and the distance in feet equals 33,000 foot- 
pounds of work per minute. AppHed to an engine, there- 
fore, the horse-power is purely a measure of mechanical 
work. As a boiler cannot perform mechanical work 
directly, its rating in horse-power must have some other 
meaning than in the case of engines. As work at the rate 
of one horse-power has a certain heat equivalent per unit 
of time, this heat equivalent to the energy of one horse- 
power per minute — that is, to 33,000 foot-pounds — might 
be thought to be the boiler capacity intended by a rating 
of one horse-power. One foot-pound is equivalent to 
.001285 heat unit, so that a mechanical horse-power 
equals .001285 x 33,000 = 42.4 heat units per minute. 
The horse-power unit, as applied to boilers, however, has 
an entirely different meaning, or, in fact, two meanings. 

A horse-power in boiler capacity is taken to be 
some rate of steam production; it is also taken to 
indicate certain sizes and proportions of boiler parts. In- 
asmuch as engines in practical use vary as much as three 
or four times in the amount of steam required per horse- 



LIGHT, HEAT AND POWER. 55 

power hour of work, the rating of a boiler in the horse- 
power of its engine is very unsatisfactory. In order to 
partially avoid the disadvantages of boiler ratings in 
horse power, the American Society of Mechanical Engi- 
neers decided in 1884 to adopt as a horse-power of boiler 
capacity the evaporation of 34-5 pounds of water at the 
temperature of 212 degrees to steam of atmospheric pres- 
sure, per hour, this being called the unit of evaporation. 
The unit thus adopted is equivalent to the evaporation of 
30 pounds of water per hour from a temperature of 100 , 
degrees to steam at 70 pounds gauge pressure ; it is also 
equivalent to 33,305 heat units per hour. The adoption 
of the definition of boiler capacity by the American Soci- 
ety of Mechanical Engineers has done much to aid defi- 
nite boiler ratings, but the horse-power of boilers is often 
spoken of in a loose way. 

Even if the evaporation of 34.5 pounds of water per 
hour at 212 degrees to steam at atmospheric pressure be 
enforced in all cases as the measure of one horse-power 
in boiler capacity, it is not clear that the use of the term 
horse-power in boiler ratings has any advantage. As the 
sole purpose of a boiler is to transfer the heat of combus- 
tion to its contained water or steam, the most obvious 
rating is one based directly on the number of heat units 
imparted to the water or steam per hour, or the pounds 
of water heated one degree per hour. If a larger unit of 
boiler capacity is wanted, the evaporation of one pound 
of water per hour at 212 degrees to steam at air pressure, 
which requires 965.7 heat units, may well be chosen for 
the purpose. Such boiler ratings would simplify the se- 
lection of boilers for heating systems, and also for engines 
of any capacity working at any pressure. In steam and 
hot water heating the results of calculations as to required 



56 LIGHT, HEAT AND POWER. 

service are readily obtained in terms of heat units or of 
pounds of steam per hour, and these are at once the boiler 
capacities desired. The fact that boiler capacity is rated 
in horse-power, each corresponding to the evaporation of 
30 pounds of water per hour, at 100 degrees to steam at a 
gauge pressure of 70 pounds, is of no advantage over a 
direct rating in heat units when the feed water is at a dif- 
ferent temperature, the gauge pressure has some other 
value, or the engine does not require 30 pounds of steam 
per horse-power hour. For any other conditions than 
those included for the feed water, gauge pressure and 
engine economy in the definition of boiler horse-power, 
the nominal power of the engine and boiler will not coin- 
cide, and the boiler capacity must be reduced to its actual 
value in heat units per hour. 

Take an example that may well occur in practice, 
where boiler capacity is necessary to supply an engine of 
100 indicated horse-power that consumes 20 pounds of 
steam per horse-power hour at a gauge pressure of 125 
pounds, where the feed water is heated to 212 degrees 
before entering the boiler. 

Obviously the horse-power rating on the above basis 
of the boiler necessary for this case cannot coincide with 
that of the engine, but the heat in the steam sent to the 
engine must be computed to find the boiler capacity, and 
then, if the boiler is to be specified in horse-power terms,' 
the boiler heating capacity must be reduced to these 
terms. The above engine, when operating at full capac- 
ity, requires 100 x 20 = 2,000 pounds of steam per hour. 
To evaporate one pound of water of 212 degrees tem- 
perature to steam of 125 pounds gauge pressure requires 
1,008 heat units, so that the boiler capacity for the present" 
engine must be 1,008 x 2,000 = 2,016,000 heat units per 



LIGHT, HEAT AND POWER. 6T 

hour. As previously defined, one horse-power of boiler 
capacity is equivalent to the delivery from fire to water of 
33,305 heat units hourly, so that the nominal boiler capac- 
ity necessary for the loo-horse-power engine is found 
from 2,016,000 -^- 33,305 = 60 horse-power. Such use of 
the term horse-power in different senses, when applied to 
engines and boilers, is obviously liable to lead to misun- 
derstandings, to say nothing of the additional calculation 
it involves. As steam engines are usually rated to con- 
sume a certain weight of steam per hour under a given 
pressure at full load, it is very convenient to specify 
boilers that will evaporate the required weight of steam 
from water at the lowest temperature the feed will ever 
reach, and to the necessary pressure, making a small 
allowance for leakage. 

It is not always possible to foresee the temperature to 
which feed water m.ay be raised in any particular case, and 
it is good poHcy to have a boiler of somewhat greater 
capacity than is absolutely necessary. For these reasons 
it is a good practical rule when specifying a boiler to dis- 
regard the possible effect of heated feed water and require 
a boiler that will yield the necessary weight and pressure 
of steam from water of 32 degrees temperature. This prac- 
tice can lead to no excessive increase of boiler capacity 
beyond the necessary point, because only 181 heat units 
are necessary to raise the temperature of one pound of 
water from 32 to 212 degrees Fahrenheit, while 966 units 
are necessary to evaporate the water under air pressure. 
At most, therefore, not more than 181 -f- (181 + 966) = 
16 per cent, of the heat necessary to change water at 32 
degrees to steam at any pressure above the air can be 
suppHed by heating the feed water up to 212 degrees. 
Not more than 16 per cent, of boiler capacity can be 



58 LIGHT, HEAT AND POWER. 

omitted if feed water is heated to 212 degrees, and this 
per cent, is hardly enough for a good margin. Where 
boilers are used entirely for steam heating at little more 
than atmospheric pressure, on the gravity system, the 
return water is usually nearly up to the 200 degree point, 
so that a capacity to evaporate the required weight of 
steam per hour from water at 32 degrees gives about 15 
per cent, margin. If the water from radiators is not re- 
turned to the boiler at all, or only after it has fallen to a 
comparatively low temperature in traps, more capacity 
beyond that necessary to evaporate the necessary amount 
of water from 212 degrees should be provided. For hot 
water boilers, it is convenient to specify a capacity to 
raise the temperature of the weight of water necessary 
to pass through the heating system per hour a some- 
what greater number of degrees, say, 10 to 20 per cent, 
more than the water it is intended to cool in periods of 
the greatest demand. 

Thus far the capacity of boilers has been treated as to 
the direct effect to be produced, but this is not usually the 
most satisfactory way to specify boiler capacity. The 
heating effect that may be transmitted by any boiler to it§* 
contained water and steam depends, of course, on the size 
and proportion of its parts, but this effect also depends in 
large measure on the quality of the fuel used, the skill 
with which the boiler is fired, the draught available, and 
the degree of efficiency maintained. 

Where the capacity of a boiler is to be decided by lit 
performance, the kind of fuel, the draught and the effi- 
ciency should also be specified, else contractors can 
hardly be expected to make the same assumptions on 
these points. 

A more direct and simple way to specify boiler capacity 



LIGHT, HEAT AND POWER. 59 

is to fix the more important dimensions of the parts that 
determine it. The heat of combustion is transferred to the 
water and steam of boilers in two ways, by contact and 
by radiation. The amount of heat that may be imparted 
to the contents of the boiler in a given time depends, 
among other factors, directly on the amount of surface in 
contact with the water on one side and exposed to the 
action of the fire and hot gases on the other. In like man- 
ner the amount of fuel that may be consumed under a 
boiler, other factors remaining constant, depends directly 
on the area of the grate surface. The heat that may be 
transmitted to the water of a boiler by a unit of heating 
surface under definite conditions, like the amount of fuel 
that may be burned per square foot of grate surface, has 
been determined by experience. 

For a single type of boiler as much as lo pounds of 
water may be evaporated from and 2X212 degrees by each 
square foot of heating surface per hour, or, on the other 
hand, a square foot of heating surface may be allowed for 
each two pounds of water to be hourly evaporated. It 
may be advisable to burn as little as eight pounds of coal 
per square foot of grate surface per hour where the 
draught is light and a slow rate of combustion necessary. 
On the other hand, where a very strong draught is avail- 
able and rapid combustion necessary, 40 or more pounds 
of coal may be burned on each square foot of grate 
hourly. In order to determine which of these widely dif- 
ferent rates of work for heating surface and grate surface 
is desirable in a given case it is necessary to consider the 
causes of these differences. 

That part of the boiler heating surface above the grate 
and surrounding the fire receives a large amount of heat 
by direct radiation from the incandescent fuel, besides that 



60 LIGHT, HEAT AND POWER. 

imparted to it by direct contact with the hot gases. This 
part of the heating surface above the fire is therefore more 
effective than any other, and a boiler in which the propor- 
tion of surface exposed to direct radiation from the fuel 
is large may be expected to show a high rate of evapora- 
tion under favorable conditions. The boiler surface be- 
yond the firebox derives its heat from the gases of com- 
bustion, and the heat transmitted to the water depends 
directly on the temperature of these gases. In the fire- 
box gases may have a temperature of 2,000 degrees Fah- 
renheit or more, but as these gases flow through the tubes 
or over the boiler surface the heat they impart to it re- 
sults in a gradual fall of their temperature. It follows that 
the more extended the boiler surfaces over which the 
gases of combustion pass the smaller will be the amount 
of heat transmitted to the water by each square foot of 
surface, on an average, because the rate at which the 
gases give up heat depends on the difference between 
their temperature and that of the heating surface. A high 
rate of evaporation is often obtained per square foot of 
heating surface in boilers by so limiting their surfaces that 
the average temperature of the gases, and consequently 
the temperature at which they escape to the chimney, is 
high. Such a construction gives a boiler cheap as to first 
cost per unit of capacity, but very expensive in subse- 
quent operation where fuel must be paid for at ordinary 
prices. 

As the heat of combustion is largely imparted to the 
gases, the loss of the gases while they are at a high tem- 
perature means the waste of a considerable per cent, of the 
coal consumed. For nearly all cases, save where the cost 
of fuel is an unimportant item, the heating surface of 
boilers should be so proportioned that the maximum 



LIGHT, HEAT AND POWER. 61 

practicable portion of their heat may be extracted from 
the gases. A Hmit to the extraction of heat from the gases 
of combustion is set by the temperature of water and 
steam in any particular boiler. It is not profitable to so 
extend the heating surface of a boiler that the gases are 
reduced to the temperature of its contents before they 
escape, as the rate at which heat is transmitted from the 
gases to the water decreases more rapidly than the differ- 
ences in the temperatures of these two bodies. 

While grate surface is an essential factor in boiler 
capacity, the relation between the area of a grate and the 
capacity of its boiler for efficient operation is much more 
variable than the relation of heating surface to the rate of 
evaporation. A boiler may give exactly equal results as 
to capacity and efficiency with grate surfaces that vary as 
much as 300 or 400 per cent, in area. To rate a boiler by 
the surface of its grate alone is therefore absurd. Grate 
surface should be considered not as a measure of boiler 
capacity, but as a thing to be determined by the capacity 
in connection with the conditions under which combus- 
tion takes place in the furnace. 

The heating surface of a boiler adds largely to the cost, 
as it is extended, but grate surface cost is comparatively 
small. It is therefore possible to make a cheap boiler 
with extensive grate surface and large capacity, though 
the heating surface is relatively very small; but such a 
boiler is necessarily inefficient, because the gases of com- 
bustion do not have time to give up their heat before 
they escape. The two factors that largely determine the 
proper extent of grate surface, compared with heating 
surface, are the quality of fuel used and the available draft. 
For coals low in ash a very wide range of variation in the 
weight consumed per square foot of grate hourly is allow- 



62 LIGHT, HEAT AND POWER. 

able if the draft is varied accordingly. In other words, 
the weight of coal that may be burned per square foot of 
grate hourly depends on the thickness of the fire, and this 
in turn on the draft pressure that can be had to force air 
through the bed of coal. With moderate pressures, such 
as are usually present where natural or chimney draft is 
employed alone, thin fires, a slow rate of fuel consumption 
per square foot of grate and a comparatively large grate 
area are necessary. If mechanical draft is available to any 
desired pressure, the thickness of fires may be largely in- 
creased and the grate area held at a low figure if the 
amount of air necessary for perfect combustion is forced 
through the fuel. When the coal employed has a large 
per cent, of ash it may be impossible to get the required 
amount of air through a thick fire with even a draft o! 
high pressure, especially if the coal ash has a strong ten- 
dency to clinker. If shaking grates or some other ar€ 
employed to get rid of the ash as fast as the coal is burned, 
thick fires may be economically employed even where a 
large portion of ash is present. 

When the available draft pressure is small, as is usually 
the case where a chimney is the only source, thick fires 
and high rates of combustion per square foot of grate sur- 
face are sure to result in poor economy, because sufficient 
air for complete combustion will not be forced through 
the coal. As a result of too little air, the gases from the 
coal are only partly burned and escape with much of theif 
fuel value undeveloped. On the other hand, a very 
strong draft, with thin fires, may result in even less capac- 
ity and economy than do thick fires and low pressure 
draft. A draft of high pressure may force many times the 
required amount of air through a thin bed of fuel, and 



LIGHT, HEAT AND POWER. 63 

thus greatly reduce the temperature of the gases of com- 
bustion and their effect on the heating surfaces. 

It should now be evident that the heating surface 
comes the nearest to a true measure of boiler capacity 
where a given degree of efficiency is to be maintained. 
True it is, as pointed out, that a boiler of small heating 
surface may be made to show a relatively large capacity, 
because the escaping gases have a very high average tem- 
perature while they are in contact with the plates; but 
this large output per unit of heating surface can only be 
obtained at the expense of efficiency. The deposit of soof 
on the fire side of the heating surfaces of boilers and the 
mineral incrustations on the water sides, as also the ten- 
dency of the gases of combustion to flow more rapidly 
over some of the surfaces than over others, all interfere 
to some extent with the relation between surface area and 
boiler capacity. These conditions, however, admit of pre- 
vention or cure, and do not change the broad fact that 
boiler capacity depends on the area of heating surface. 
When a given capacity and efficiency are required m a 
boiler a relation is established between the output, the 
area of heating surface and the rate at which coal is 
burned in its furnace. The area of the grate surface is not 
included in these requirements. It is only when the avail- 
able draft is specified and the quality of coal named in 
connection with the capacity and efficiency that the area 
of grate is fixed. A given weight of coal burned per hour 
may easily give equal results with the same boiler when 
it forms a thick fire on a small grate with high draft pres- 
sure as when spread over a much larger grate for a low 
pressure draft. 

As has been pointed out, some parts of the heating sur- 
faces of boilers are more effective than others, because of 



64 LIGHT, KEAT AND POWER. 

their positions, while further differences may arise during 
operation from deposits of soot or incrustations. Any 
system of surface measurement that undertook to make 
allowance for all of these differences would be too com- 
plicated for general appHcation. The best way, there- 
fore, to compute the heating surface of a boiler is to in- 
clude all surfaces in it that have the fire or hot gases on 
one side and water on the other. In boilers of good pro- 
portions and design the differences in effectiveness be- 
tween the several parts of the heating surfaces nearly off- 
set each other, so that the total surface subject to the 
action of fire and water in each is usually a fair basis of 
comparison. 

Aside from the very small boilers used for house heat- 
ing and made in a great variety, of forms, those in general 
use may be divided into five main classes — the plain 
cylindrical, the flue, the horizontal and vertical tubular, 
the horizontal internally fired, and the water-tube boilers. 
The construction and setting of these several types of 
boilers determine the heating surface of each. That part 
of the boiler surface that has fire or hot gases on one side 
and steam on the other cannot fairly be taken as a part of 
the heating surface, because the amount of heat that the 
steam will take from hot plates in contact with it is verv 
small compared with the heat absorbed by water. Under 
normal conditions of operation, plain cyHndrical boilers 
are usually so supplied with water that about two-thirds of 
their side surfaces are in contact with it. The setting of 
these boilers in brick work leaves the portion of their 
sides that are in contact with water and about one-half of 
one end subject to the action of flames and hot gases. 
The rule to find the heating surface for a plain cylindrical 
boiler is thus: Multiply the length in inches by two-thirds 



LIGHT, HEAT AND POWER. 65 

of the circumference in inches, and to this product add 
the area in square inches of one-half of one end of the 
boiler; divide this total by 144 to get the heating surface 
of the boiler in square feet. 

Cylindrical boilers with one or two flues extending from 
one head to the other are usually supplied with water and 
mounted in brick work in much the same way as are plain 
cylindrical boilers, except that the gases leave the boiler 
at the front or furnace end after passing through the flues. 
The rule for heating surface in this type of boiler is there- 
fore: Multiply the length of the boiler by two-thirds of its 
circumference, all taken in inches; then multiply the 
length of each flue by its circumference, and this product 
by the number of flues; next find the area in square inches 
of one of the boiler heads; take one and one-half times 
this area and from this product subtract twice the end 
area of all of the flues; to the remainder add the product 
representing the outside cylindrical heating surface, and 
that representing the combined surface of the flues; divid6 
this total sum by 144 to get the area of the boiler heating 
surface in square feet. 

Vertical tubular boilers are internally fired, and the fire- 
box is made up of surfaces with water on their other sides. 
In this type of boiler the gases of combustion pass upward 
through the tubes and emerge at the top. The rule to 
find the heating surface of the vertical tubular boiler is: 
Multiply the circumference of the firebox by its height 
above the grate, all dimensions in inches; multiply the 
circumference of one tube by its length to the water line, 
and this by the number of tubes; to the sum of these two 
products add the area of the lower tube sheet, in square 
inches, and divide the total by 144 to get the area of heat- 
ing surface in square feet. 



6G LIGHT, HEAT AND POWER. 

Horizontal tubular boilers are usually set in brick work 
similar to that used with the plain cylindrical, except that 
an up-take is provided at the front end, so that the gases, 
after passing to the rear of the boiler along its outside and 
then entering the tubes and flowing to the front end, may 
there escape. The rule to find the heating surface of the 
horizontal tubular boiler is: Multiply the length of the 
boiler by two-thirds of its circumference, all taken in 
inches; multiply the circumference of one tube by its 
length, and this by the number of tubes ; to the sum of the 
products thus found add two-thirds of the area of one tube 
sheet twice; divide the total sum by 144 to get the heating 
surface in square feet. 

Internally fired horizontal boilers, as used on land, are 
known as the Cornish and 'Lancashire types, and are 
much more generally used in England than in the United 
States. The Cornish boiler has one every large and the 
Lancashire has two somewhat smaller internal flues from, 
end to end. These boilers are set in brick work like the 
plain cylindrical and tubular in some respects. Grates 
and fires for these boilers are placed in one end of the 
flues and the gases of combustion pass first through the 
entire flue length to the rear end, then back to the front 
of the boiler along its sides and subsequently to the rear 
again and underneath. The rule to find the heating sur- 
face for this type of boiler is: Multiply the total length by 
two-thirds of the outside circumference of the boiler, all 
dimensions to be taken in inches; multiply the circumfer- 
ence of one of the flues by its length and by the number 
of flues; to the sum of these products add two-thirds of 
the area in square inches of one of the boiler heads; then 
subtract the sum of the cross-sectional area of the flue or 



LIGHT, HEAT AND POWER. 67 

flues and the flue area beneath the grates; divide the 
remainder by 144 to get heating surface in square feet. 

The locomotive type of boiler and also the marine or 
Scotch boiler belong to the class that are internally fired. 
Each of these boilers partake of the construction in the 
tubular boiler, inasmuch as they have internal fire tubes. 
Neither the locomotive nor marine boiler uses the outside 
surface for heating the contained water by passing the 
gases of combustion over it, but each absorbs its heat 
through the internal firebox, combustion chamber and 
fire tubes. These boilers vary somewhat in construction, 
but their heating surface can be readily computed by an 
application of the principles involved in the rules given 
for tubular and internally fired boilers. Boilers of the 
locomotive type are occasionally used in buildings, but 
marine boilers are seldom employed apart from ships. 

Water-tube boilers are mostly externally fired, and the 
tubes have the water on their insides instead of on their 
outsides, as in the tubular boiler. These water tubes have 
their ends connected to one or more water and steam 
cylinders, made like small cylindrical boilers. Water- 
tube boilers are made in a large variety of forms, but the 
same principles as to heating surface apply to all. The 
rule to find the heating surface of a water-tube boiler is: 
Multiply the circumference of one tube by the length of all 
of the tubes exposed to the flames or gases ; multiply one- 
half of the circumference of the steam and water cylinder 
by its length, and this by the number of these cylinders, 
if there are more than one; add the products thus found 
and divide their sum by 144 to get the area of the heating 
surface in square feet. 

Having in mind what the heating surface of a boiler 
really is, we are in a position to note the relation between 



68 LIGHT, HEAT AND POWER. 

heating surface and boiler capacity. Grate surface in any 
boiler furnace is obviously the area of the grate where the 
fuel is burned, and its amount in square feet is obtained 
by a simple multiplication of the length and width. 

If boiler performance is to be obtained and stated in 
pounds of water evaporated from and at 212 degrees per 
hour or in heat units delivered to the contained water per 
hour, as is most convenient and accurate, it is desirable to 
know the average capacity of each square foot of heating 
surface in terms of heat transfer or evaporative effect per 
unit of time. The capacity of one square foot of boiler 
surface as to rate of heat transfer is necessarily a matter 
of observation and experience. No general result can be 
stated that applies with minute accuracy to every case, but 
an average capacity per square foot of heating surface in 
any well designed and constructed boiler has been found 
that makes efficient operation possible. This capacity is 
the evaporation of three pounds of water per hour from 
and at 212 degrees per square foot of heating surface, on 
an average. As 965.7 heat units are absorbed by the 
evaporation of one pound of water at 212 degrees to 
steam of the same temperature, which must be of atmos- 
pheric pressure, the evaporation of three pounds of water 
corresponds to a transfer from fire to water of 965.7 x 3 = 
:2,897.i heat units hourly per square foot of heating sur- 
face. If not more than 0.3 pound of coal is burned in the 
boiler furnace per square foot of its heating surface per 
hour, a, high efficiency is easily attainable with suitable 
draft and good firing, and the flue gases may be reduced 
in temperature to about 450 degrees. Thus, if coal de- 
velops 13,000 heat units per pound on perfect combus- 
tion, if 0.3 pound is burned hourly per square foot of heat- 
ing surface, and if 2,897 heat units are transmitted to the 



LIGHT. HEAT AND POWER. 69 

water by each square foot of surface per hour, the boiler 
efficiency is 2,897 ^~ (i3>ooo x .3) = 74 per cent. 

Of course, the allowance of one square foot of heating 
surface for each three pounds of water to be evaporated 
hourly does not ensure efficient operation, as too much or 
too little draft, or bad firing, may result in imperfect com- 
bustion of the fuel or in too great velocity of the gases. A 
greater allowance of heating surface than one square foot 
for each three pounds of water to be evaporated can effect 
but little gain in economy for power boilers, because their 
temperatures do not allow the gases to cool much below 
450 degrees. 



CHAPTER VII. 

COMBUSTION OF FUELS AND BOILER EFFICIENCY. 

The efficiency of a furnace and boiler is found when the 
heat imparted to water or steam from a certain amount of 
fuel is divided by the number representing the total 
amount of heat that this fuel can develop on 
perfect combustion. Perfect efficiency which is not 
attainable imphes that complete combustion takes 
place with all the fuel used . and that all the heat of 
this combustion is transferred to the water or steam of 
the boiler. One pound of pure carbon completely burned 
to carbonic acid yields 14,500 heat units. As one pound 
of water evaporated from and at 212 degrees absorbs 966 
units of heat, the pound of pure carbon consumed with a 
furnace and boiler of perfect efficiency will evaporate 14,- 
500 -^ 966 =15 pounds of water under these conditions. 
Experiments have shown that an efficiency of 80 per 
cent, is about the highest that can be reached with the 
best boilers and furnaces, so that an evaporation of 15 x 
.80 = 12 pounds of water from and at 212 degrees may 
be had per pound of pure carbon. 

None of the ordinary fuels consist entirely of carbon, 
but coke contains about 90 per cent, of carbon and 10 per 
cent., sulphur, moisture and ash. One pound of good 
coke, therefore, when burned under a boiler of the 
highest efficiency, evaporates 12 x. 90 =10.8 pounds of 
water from and at 212 degrees. If the efficiency of the 



LIGHT. HEAT AND POWER. 71 

furnace and boiler is at the more common figure of 65 
per cent., one pound of coke yields an evaporation, un- 
der the conditions named of 15X .65X .90 = 8.77 pounds 
of water. 

If the combined efficiency of furnace and boiler drops 
to 50 per cent., the water that may be evaporated from 
and at 212 degrees by the combustion of one pound of 
coke is only 15 x .90 x .50 = 6.75 pounds. The weight of 
water evaporated with furnaces and boilers of various 
efficiencies when other fuels than coke are used may be 
readily calculated from the figures for the heating pow- 
ers of these fuels per pound. 

The combined efificiencies of furnaces and their boilers 
are less than unity, because of imperfect combustion of 
the fuels, excessive air supplies which reduce the tem- 
peratures of the gases, the escape of gases from the boiler 
surfaces at high temperature, the heat absorbed by the 
evaporation of water in the fuels, and the radiation and 
conduction of heat from the boiler, furnaces and settings. 

As a boiler and its settings are much above the sur- 
rounding air in temperature while in operation, a constant 
loss of heat takes place from all their external surfaces. 
The extent of this heat loss varies with the extent to 
which the boiler covering or setting provides a good heat 
insulation, with the temperature of the boiler room 
and with the arrangement of the boilers. All losses 
of heat not otherwise accounted for are frequently 
charged to radiation and conduction from the exterior 
surfaces. This is only a rough way to determine the 
losses in question, as it covers up all errors from the 
analysis of the fuel to the temperature of the escaping 
chimney gases. The heat lost from the exterior surface 
of a boiler and its setting may be determiined directly if a 



72 LIGHT, HEAT AND POWER. 

small portion of the grate surface is bricked off and pro- 
vided with just enough fire to maintain steam at the 
desired or usual pressure, while none is drawn from the 
boiler. A record of the coal burned per hour to simply 
maintain the steam pressure while no steam is taken from 
the boiler represents the consumption due to losses from 
the exterior surfaces and settings. After the efficiency of 
the boiler has been determined the actual loss in heat units 
from its exterior surfaces can be found by means of the 
recorded consumption of coal to simply maintain the 
steam pressure. All water contained in the fuel neces- 
sarily reduces the combined efficiency of the furnace and 
boiler, because this water must be converted into steam 
and raised to the temperature of the fire. Coal and coke 
that is kept under cover often contains 3 to 5 per cent, of 
water by weight, and if exposed to the weather the pro- 
portion of water may rise to 10 per cent, or more. The 
loss of efficiency through the use of wet coal or coke may 
be serious, as the following figures show: In the case of 
coke containing 10 per cent, of moisture, and also 10 per 
cent, of ash, as before mentioned, the total heating power 
per pound on perfect combustion amounts to 14,500 x .80 
= 11,600 units. To evaporate one pound of water in 
the coke from and at 212 degrees requires 966 heat units, 
and about 250 units per pound are necessary to raise the 
water to 212 degrees, and also the resulting steam to 
the temperature of the fire, a total of 1,216 units of heat. 
The 10 per cent, of moisture contained in one pound of 
this coke thus absorbs 121 -7- 11,600^ about 10 per cent. 
of its heating capacity and lowers the efficiency by this 
figure. 

If wet coal or coke is purchased there is thus a loss not 
only of the weight of fuel represented by the contained 



LIGHT, HEAT AND POWER. 73 

water, but also a further loss to evaporate this water. 
Aside from their contained steam, chimney gases repre- 
sent two distinct kinds of losses — those due to the tem- 
perature of these gases, and those that result from incom- 
plete combustion. In order to determine how much 
energy the chimney gases represent, it is thus necessary 
not only to take their temperature, but also to determine 
their composition by chemical analysis. Where bitu- 
minous coal is the fuel, its volatile portion is rapidly driven 
off as gas before its combustion, and if this gas escapes 
unburned a large portion of the total heating power of the 
coal is lost. If the combustible portion of the fuel used 
consists entirely of pure carbon, as is nearly the case for 
anthracite coal, as well as for coke, gas is formed only as 
the oxygen of the air unites with the carbon to form car- 
bonic acid. One pound of carbon combines with two and 
two-thirds pounds of oxygen to form three and two-thirds 
pounds of carbonic acid gas. If the supply of air to the 
furnace is insufficient, the carbonic acid in con- 
tact with the incandescent solid carbon combines 
with an additional quantity of carbon to form 
carbonic oxide. The carbonic oxide contains car- 
bon and oxygen in the proportion of two pounds 
of carbon to two and two-thirds pounds of 
oxygen; or, in other words, three and two^thirds pounds 
of carbonic acid unite with one pound of carbon to form 
four and two-thirds pounds of carbonic oxide. The space 
occupied by the three and two-thirds pounds of carbonfc 
acid is just equal to the space required for the two and 
two-thirds pounds of oxygen that enters it; but when 
three and two-thirds pounds of carbonic acid unite with 
one pound of carbon to form four and two-thirds pounds 
of carbonic oxide, this oxide expands to twice the volume 



74 LIGHT, HEAT AND POWER. 

of the carbonic acid entering into it. One pound of car- 
bon yields 14,500 heat units when it unites with two and 
two-thirds pounds of oxygen to form carbonic acid, and 
this is the maximum heating effect that can be got by the 
combustion of carbon. If, owing to an insufficient supply 
of air, the carbonic acid unites with a weight of carbon 
equal to that which it already contains, carbonic acid is 
formed, in which one pound of carbon is combined with 
one and one-third pounds of oxygen, and the heat result- 
ing from this combination is only 4,400 units per pound 
of carbon. It thus appears that if carbonic oxide instead 
of carbonic acid is the final result of the combustion of 
carbon, the heat obtained per pound of carbon is less than 
one-third as great as that available where carbonic acid is 
the ultimate product. 

This difference in heating 'effects is due to the absorp- 
tion of energy to expand the gas and convert double the 
weight of carbon from a solid to a vapor per unit of oxy- 
gen consumed in the case of carbonic oxide. If sufficient 
air is supplied to carbonic oxide, two and one-third 
pounds of this gas, or the amount containing one pound 
of carbon, unites with one and one-third pounds of oxy- 
gen to form three and tv/o-thirds pounds of carbonic acid, 
the original product of the combustion. The two and 
one-third pounds of carbonic oxide on combustion with 
one and one-third pounds of oxygen yield 10,100 heat 
units, which, added to the 4,400 heat units liberated by 
the formation of the two and one-third pounds of car- 
bonic oxide, gives the total heat per pound of carbon con- 
sumed as 14,500 units, as before. From the foregoing 
facts it is evident that complete combustion of the carbon 
in fuel is of the highest importance for boiler economy. 
This com.plete combustion can only be had with an ample 



LIGHT, HEAT AND POWER. 75 

supply of air to yield the necessary oxygen. Experi- 
ence has shown that complete combustion cannot be at- 
tained with an air supply that contains only the amount 
of oxygen actually combining with the carbon burned. 
It is therefore the practice to admit more air to 
furnaces than that containing the weight of oxy- 
gen to be combined with the carbon of the neces- 
sary fuel. This practice may easily be carried too 
far, however, because all of the air admitted to the fire 
necessarily lowers the resulting temperature of the gases 
of combustion, and thus reduces the amount of heat that 
the boiler surfaces can extract from them. The best prac- 
tice as to air supply must therefore admit to the fuel just 
enough air to ensure complete combustion, but no more. 
Thus far fuel that consists almost entirely of pure car- 
bon as to its combustible portion has been considered. 
Anthracite coal contains 3 to 5 per cent, of volatile mat- 
ter, and this ratio increases through the semi-anthracite, 
semi-bituminous and bituminous coals up to 40 per 
cent, or more. This volatile matter consists of com- 
pounds composed of carbon, hydrogen and oxygen. 
These compounds go under the general name of hydro- 
carbons, and must pass into the gaseous state before they 
are burned. Where oxygen and hydrogen exist together 
in a fuel they unite to form steam under the influence 
of combustion in the proportion of one pound of hydro- 
gen to eight pounds of oxygen up to the point where the 
supply of either oxygen or hydrogen in the fuel is ex- 
hausted. This union of oxygen and hydrogen to form 
water or steam liberates no heat energy, but each pound 
of the steam thus formed absorbs about 1,216 heat units 
from the fire to raise its temperature and supply latent' 



76 LIGHT, HEAT AND POWER. 

heat. The carbon of the volatile compounds has an equal 
heating value per pound with that in the sohd portion of 
the fuel. After the oxygen of the volatile compounds 
has been consumed by combination with their hydrogen 
to form steam, the remaining hydrogen is available for 
fuel. One pound of hydrogen, when burned by combina- 
tion with eight pounds of oxygen, yields 62,032 units of 
heat, or more than four times the heat that can be gen- 
erated by the combustion of one pound of carbon. Hy- 
drogen is thus a most energetic fuel, but unless suitable 
precautions are taken in the use of bituminous coal a 
large part of the volatile compounds containing the hy- 
drogen escape unburned. 

This tendency for the volatile portion of semi-bitumi- 
nous and bituminous coals to escape to the chimney be- 
fore combustion can take place is due to the fact that they 
are converted into the gaseous form at comparatively 
low temperatures, are often cooled below the point of 
combustion by mixture with cold air in the furnace, an4 
that the air supply is at times insufficient to furnish oxy* 
gen as fast as it is necessary. To avoid the loss of boiler 
efificiency from the causes just named, the air should be 
heated before it is supplied to the funrace, and its quantity 
should be ample for the desired combustion. Moreover, 
the furnace, where coal with a large percentage of vola^ 
tile matter is to be burned, should have an arch of fire- 
brick a short distance above the grate in order to make 
sure that the gases will not fall below the temperature of 
combustion until after they are burned. 

Complete combustion of the fuel is the office of the 
boiler furnace, while it is the purpose of the boiler sur- 
faces to extract from the gases as much as possible of the 
heat thus generated. The temperature of the surfaces of 



LIGHT, HEAT AND POWER. 77 

a boiler are fairly constant for any given steam 
pressure, providing the supply of feed water is 
regular, but the temperature of the gases of 
combustion is a very variable quantity. Ob- 
viously, as the gases pass over the boiler surfaces and 
give up heat, their temperature is reduced. It has been 
found in practice that it is not wise to carry this reduc- 
tion of temperature for the gases much nearer than 150 
degrees to that of the steam in the boiler, because of the 
great extension of boiler surface necessary, due to the 
slow passage of heat from the gases to the water of the 
boiler when they are near the same temperature. 

The temperature of steam at 100 pounds gauge pres- 
sure is 337 degrees, so that the temperature of the gases 
of combustion cannot well be reduced much below 150 + 
337, or about 500 degrees, before they leave the surfaces 
of a boiler operated at this pressure. With 
compound engines a steam pressure of 150 pounds 
gauge may well be used, corresponding to a temperature 
for the steam of 365 degrees, and leaving the lowest de- 
sirable temperature of gases from the boiler surfaces at a 
little more than 500 degrees. Where a boiler is operated 
at a low pressure, say, of five pounds, for steam heating, 
corresponding to a temperature of 227 degrees, or for hot 
water heating at a temperature of 212 degrees, the gases 
may well be reduced to a temperature of 375 degrees be- 
for leaving the boiler surfaces. 

Taking 500 degrees as about the average temperature 
of gases escaping from boilers used for steam power pur- 
poses, it is evident that, excluding the factor of direct 
radiation from the bed of fuel on the grate, the heat de- 
rived by the boiler from its fuel is measured by the fall in 
the temperature of its gases from the time they leave the 



78 LIGHT, HEAT AND POWER. 

furnace until they escape to the chimney. The greater 
this fall of temperature the higher will be the efficiency of 
the boiler, other factors being constant. Before the fall in 
the temperature of gases can be determined the tempera- 
ture at which they leave the furnace must be known. In 
order to determine the initial temperature of the furnace 
gases it is necessary to know the amount of air entering 
the furnace per unit of time, as well as the rate at which 
fuel is consumed and its quality. 

Oxygen for the combustion of fuel necessarily comes 
from the air admitted to the furnace. As pointed out 
above, two and two-thirds pounds of oxygen are neces- 
sary for the complete combustion of one pound of carbon, 
and eight pounds of oxygen are required to burn one 
pound of hydrogen. Air is a mechanical mixture of 23 
parts of oxygen and yy parts of nitrogen by weight. It 
follows that to furnish eight pounds of oxygen to burn 
one pound of hydrogen the air that must be admitted to 
the furnace is found from 8 -^- .23 = 34.78 pounds. In 
like manner the weight of air, 2.^ pounds, necessary to 
furnish oxygen to burn one pound of carbon is found 
from 2.66 -^ .23 -f- 1 1.6 pounds. It is evident that at 
least these proportions of air must be heated to the tem- 
perature of the furnace, as must also the fuel consumed. 
As a matter of practice, a much larger proportion of air 
is necessary. 

As each pound of fuel suppHes a definite number of 
heat units on complete combustion, independently of the 
amount of air mixed with the gases of combustion, the 
temperature of the mixture of gases and air evidently 
depends on the ratio between the weight of air and fuel 



LIGHT, HEAT AND POWER. 79 

supplied to the furnace. While it is desirable that the 
initial temperature of the gases of combustion in the fur- 
nace be at a point as high as is possible above their nearly- 
fixed final temperature at the chimney, it is found in prac- 
tice that to avoid the very serious losses incident to im- 
perfect combustion the actual supply of air in any case 
must materially exceed in oxygen the chemical require- 
ments of the fuel burned. It is therefore common prac- 
tice to supply from one and one-half to twice the air to 
boiler furnaces that their actual consumption of oxygen 
in combustion with the fuel consumes. To determine the 
temperature of the products of combustion above that of 
the air, assuming all the heat to be absorbed by the gases, 
the total heat units liberated by burning one pound of the 
fuel should be divided by the sum of the products of each 
element in the furnace gases by its specific heat. The 
specific heats of the important gases concerned 
in combustion are as follows: At constant pres- 
sure, air, 0.237; oxygen, 0.217; hydrogen, 3.409; nitro- 
gen, 0.243; steam, 0.475; carbonic acid, 0.217; carbonic 
oxide, 0.247. The maximum temperature of combustion 
is obviously attained when just enough air is admitted to 
the furnace to supply oxygen for the chemical combina- 
tion. If pure carbon is the fuel used, one pound develops 
14,500 heat units. For the perfect combustion of this 
carbon two and two-third pounds of oxygen are neces- 
sary, and this oxygen is contained in air weighing 11.6 
pounds. Of this air 11.6 — 2.66 = 8.94 pounds appear 
as nitrogen in the products of combustion, the remainder 
of these products with the one pound of carbon being 
3.66 pounds of carbonic acid. The multiplication of the 



so LIGHT, HEAT AND POWER. 

weight of each of these gases by its specific heat yields 
the following results : 

Nitrogen, 8.94 x 0.243 = 2.17 

Carbonic acid, 3.66 x 0.217 0.79 



2.96 

Dividing the 14,500 heat units developed from the one 
pound of carbon by the quantity just found, shows the 
maximum temperature of combustion to be 14,500 -f- 2.96 
= 4,899 degrees above the temperature of the air and fuel 
supplied. No such temperature as this can be attained in 
regular practice, however, and the following figures, 
based on the admission of 24 pounds of air to the furnace 
for each pound of carbon burned, are given to represent 
ordinary results where the . gases absorb all of the 
heat. In this case the figures just found for free nitrogen 
and carbonic acid remain good, and to them must be 
added the value for 24 — 11.6 = 12.4 pounds of air. As 
the specific heat of air is 0.237, the quantity that must be 
added to the above divisor of the total heat combustion is 
12.4 X 0.237 = 2.94, making the divisor for the present 
case 2.94 + 2.90 = 5.90. The total heat of combustion 
divided by this last quantity yields 14,500 ^- 5.90 = 2,457 
as the temperature in degrees Fahrenheit of the products 
of combustion above that of the air. To represent about 
what might be done in the best practice if the entire heat 
of combustion went into the gases the following results 
are computed on the basis of 18 pounds of air admitted to 
the furnace for each pound of carbon completely burned. 
In this case 11.6 pounds of air will be separated into oxy- 
gen and nitrogen in order to efifect the combustion as 
above, leaving 18 — 11.6 = 6.4 pounds of air to be heated 
to the temperature of the fire. The weight of this air 



LIGHT, HEAT AND POWER. 81 

multiplied by its specific heat amounts to 6.4 x 0.237 = 
1. 5 17, which, added to the figure of 2,96 for the free nitro- 
gen and carbonic acid, gives 2.96 + 1.52 = 4.48 as the 
divisor for the total heat of combustion. The result of this 
division is 14,500 -^ 4.48 = 3,236, representing the initial 
temperature of the gases of combustion in degrees Fah- 
renheit above that of the air. Taking, then, 3,000 degrees 
above the air as about the highest initial temperature to 
be attained in the products of combustion, and 500 de- 
grees above the air as their temperature when they leave 
the boiler surfaces, the difference, or 3,000 — 500 = 2,500 
degrees, indicates the portion of the heat imparted to 
them that the gases give up to the boiler. If the gases 
yield their heat in the same ratio that they cool, which is 
practically true, the fall of temperature from 3,000 to 500 
degrees above that of the air corresponds to an extraction 
of 2,500 -^ 3,000 = .83 per cent, of the heat that has been 
imparted to them. 

If the total heat of combustion is absorbed by the re- 
sulting gases, as has thus far been assumed, the figure of 
.83 per cent, might represent the boiler efficiency, but this 
cannot be the case, for two reasons. In no case can all 
the heat of combustion be absorbed by the gases of com- 
bustion, because some of it is absorbed by the ashes 
and more is lost by radiation from the boiler and 
furnace. Aside from these losses, a large amount of heat, 
with many forms of boiler setting, passes directly from 
the bed of incandescent fuel to the boiler by radiation, 
and cannot therefore be included in the heat absorbed by 
the gases of combustion. No satisfactory general rule can 
be laid down for the proportion of the heat of combustion 
that passes from the fuel in the furnace to the boiler by 
direct radiation. In a furnace where the fuel is sur- 



S2 LIGHT. HEAT AND POWER. 

rounded on all sides above the grate by firebricks, radia- 
tion from the fuel to the boiler, which can only take place 
on straight lines, is not possible. In this case, therefore, 
the total amount of heat imparted to the boiler is meas- 
ured by the fall of the temperature of the gases while they 
are passing over its surfaces. 

For the more common case, where the fuel is sur- 
rounded in part by the heating surfaces of the boiler, from 
two-tenths to four-tenths of the total heat generated by 
the fuel will pass by direct radiation to the boiler surfaces. 
Applying suitable figures for losses of heat in the ashes 
and from boiler settings, it is possible to determine an 
approximate figure for the maximum initial temperature 
of the gases, where a part of the boiler surfaces surround 
the fuel. If a large per cent, of the boiler surface is in- 
cluded in the firebox about the bed of fuel, as in the loco- 
motive type of boiler, a relatively large ponion of the 
total heat of combustion will pass to the boiler surfaces by 
direct radiation, other things being equal. If, on the 
other hand, the amount of surface that direct radiation 
from the fire can reach is relatively small, comparatively 
little heat will pass to the boiler in this way. Other fac- 
tors remaining constant, thick fires lower the per cent, of 
total heat passing to the boiler surfaces by direct radia- 
tion, while thin fires increase this per cent., because of the 
greater radiating surface the fuel offers in proponion 
to the amount consumed. As a medium figure, 0.3 may 
be taken as that portion of the total heat developed that 
passes to the boiler by direct radiation. For the loss of 
heat in the ashes and from the boiler setting 10 per cent, 
of the total may be assumed. 

With these figures as a basis, the heat remaining to be 
absorbed by the gases is 100 — 30 — 10 = 60 per cent, of 



UnilT. HE4T AND roWRH 83 

the total atnoutU result ifig from combustion. Consulcrmg 
one poutul of pure carbon, as before, the heat now avail- 
able for the gases of combustion is 14.500 \ .6 =^ 8./00 
units. Taking the case where 18 poutuU of air is supphed 
to the furnace for each pound of carbon burned, it wa« 
found above that the amount of heat available for the 
gases must be divided by the factor 4.48 to determine the 
initial temperature of the products of combustion. This 
division shows that the temperature of the gases will be 
8.7l10-^- 4.48^= 1.U42 degrees I'ahrndicit above that of 
the air and fuel supplied to the furtiace. If now the gases 
of combustion leave the boiler at a temperature of 500 
degrees above that of the outside air, as tiiight well b^ 
the case with the outside air at i^ero temperature, the pof* 
tion of their contained heat given by the gases to the 
boiler surfaces is (1.94^ — 500) -\- 1.94^ = 74 per cent. 
As only 60 per cent, of the total heat produced by the 
combustion of the pound of carbon is imparted to the 
gases in this case, these gases deliver to the boiler .60 x 74 
= 44 per cent, of this total, tt was assumed at the start 
that ^K^ per cent, of the total heat of combustion went to 
the boder as direct radiation, so the cfFicicncy of the boiler 
and furnace for the present case is the sum of .44 + .^o == 
74 per cent. The loss of j6 per cent, is divided between 
those by radiation from the setting and those in the escap- 
ing gases. Ten per cent, was allowed at the start for loss 
of heat by radiation and in the ashes. The portion that 
may be lost with the tlue gases is therefore 26 — lo = 16 
per cent. This last figure may be arrived at by consider- 
ing that the gases absorb as a total only 60 per cent, of 
the heat of combustion, and 26 per cent, of this amount 
escapes to the chimney, so that the chinmey loss of heaf 
must be 26 x .6q= 15.6 per cent. 



84 LIGHT, HEAT AND POWER. 

This efficiency figure for the boiler and furnace, namely, 
74 per cent., has been obtained on the assumption that 
the pound of carbon considered is perfectly burned, but it 
is hard to obtain perfect combustion of all the fuel in even 
the best furnaces, so that the figure for efficiency is often 
lowered 3 to 5 per cent, because the fuel is not completely 
burned. In order to raise the efficiency in this case from 
74 to 80 per cent., or about the highest figure it has thus 
far been practicable to obtain, the loss by radiation from 
the boiler and furnace settings must be reduced a little by 
better heat insulation on these parts. It will also be 
necessary either to reduce still further the amount of air 
admitted to the furnace per pound of fuel without causing 
imperfect com.bustion, or else to increase the heat ex- 
tracted from the gases of combustion, as may be done by 
means of an economizer. 

The fuel thus far considered has been assumed to con- 
sist, as to its combustible portion, of pure carbon, as is 
true for coke, and nearly so for the best grades of anthra- 
cite coal. Semi-bituminous coal is much more generally 
used than anthracite for the furnaces of power boilers, and 
the results obtained with the former fuel differ somewhat 
from those had with coke and anthracite coal. Take, for 
example, a dry coal of which the combustible portion 
contains 82 parts carbon, 10 parts hydrogen and 8 part's 
oxygen. Under the influence of combustion all the oxy- 
gen in this fuel will unite with enough hydrogen to form 
water. As water consists of 8 parts by weight of oxygen 
to I of hydrogen, the loss of hydrogen in this case will be 
.08 -^- 8 = .01. pound, and the hydrogen remaining for 
combustion is .09 pound. The heating, power of this 
pound of combustible is thus for the carbon 14,500 x .82 
= 11,890 units, and for the hydrogen 62,032 x .09 =5 



LIGHT, HEAT AND POWER. 85 

5,582 units, a total of 17,472 heat units. The oxygen 
that must be suppHed from the air for the combustion of 
this fuel is for the carbon 2.66 x .82 = 2.18 pounds, and 
for the hydrogen 8.0 x .09 = 0.72 pounds, making the 
total weight of oxygen = 2.90 pounds. As air contains 
23 per cent, of oxygen by weight, the amount of air neces- 
sary to supply just enough oxygen for the chemical com- 
bustion in this case is 2.9 -f- .23 = 12.6 pounds. Of this 
air 12.6 — 2.9 = 9.7 pounds is reduced to free nitrogen by 
the combustion. With good management of the furnace, 
perfect combustion may be effected by the use of 50 per 
cent, more air than that necessary to supply oxygen, so 
that the total air entering the furnace in this case per 
pound of combustible may be 12.6 x 1.5 = 18.9 pounds. 
The free air to be raised to the temperature of the prod- 
ucts of combustion in this case is thus 6.3 pounds. For 
each pound of combustible the weight of water formed 
by the contained oxygen and hydrogen is 0.08 + o.oi = 
0.09 pound, and to this should be added the weight of the 
hydrogen burnt with oxygen from the air, the total is 
0.09 + (8 X .09) = 0.81 pound of steam. To determine 
the temperature of the products of combustion the weight 
of air, carbonic acid, nitrogen and steam must each be 
multiplied by its specific heat, and then the sum of these 
products used as a divisor for that part of the total heat 
of combustion that is available for absorption by the 
gases. The weight of carbonic acid for this case is 0.82 + 
2.18 = 3.00 pounds, and the product by its specific heat 
3 X .217 == .651 ; for air the product is 6.3 x .238 = 
1.499; ^or the nitrogen 9.7 x .245 = 2.436; for the steam 
0.81 + .48 = 0.388, making a total divisor of 3.974. The 
total heating capacity for this pound of combustible was 
found above to be 17,472 heat units, and of this 10 per 



86 LIGHT, HEAT AND POWER. 

cent, may be allowed for loss by radiation from the boiler 
and furnace setting and 30 per cent, for transfer to the 
boiler by direct radiation. There remain 17,472 x .60 = 
10,483 heat units for absorption by the products of com- 
bustion. Dividing this last number by the factor 3.97, 
above found, yields 10,483 -f- 3.97 == 2,643, representing 
the initial temperature of the products of combustion 
above that of the outside air in degrees Fahrenheit. If 
these gases are cooled by the boiler to 500 degrees above 
outside air, they represent a loss of 500 -f- 2,643 = ^9 
per cent, of the heat imparted to them. 



CHAPTER VIII. 

HEATING POWERS OF FUELS. 

The heating power of the fuel consumed in any case 
must be known before the efficiency of the boiler with 
which it is used can be determined. Coal or other fuel 
may have its heating value per unit of weight determined 
by chemical analysis or by combustion in a calorimeter. 
The practical heating value of any fuel may obviously be 
found by actual trial of it with a boiler, but such a trial 
shows only the result that may be attained with the par- 
ticular boiler used, and cannot determine the boiler effi- 
ciency unless the total heating value of the fuel is previ- 
ously known. 

A chemical analysis of coal shows the relative propor- 
tions of carbon, hydrogen, oxygen, water and ash that it 
contains. The extent to which the carbon and hydrogen 
yield heat per unit of weight on perfect combustion is 
known, and the heating value of a pound of coal contain- 
ing certain portions of these elements is thus easily calcu- 
lated. Water and ash, of course, contribute nothing to 
the heat that may be derived from coal. 

A formula may be readily constructed to give the heat- 
ing value of a certain coal per pound when the chemical 
analysis of the coal is known. Such a formula expresses 
what is known as Dulong's law, and is : Heat units = 14,- 

O 

500 C + 62,000 (H ), in which C stands for the frac- 

8 
tion of a pound of carbon, H the fraction of a pound of 
hydrogen and O the fraction of a pound of oxygen found 
in one pound of coal. The numbers 14,500 and 62,000 



88 LIGHT. HEAT AND POWER. 

represent the heat units Hberated by the complete com- 
bustion of one pound of carbon and of one pound of 
hydrogen, respectively, as determined by experiment. 

A calorimeter consists essentially of a closed iron ves- 
sel, adapted to receive a quantity of fuel and oxygen and 
immersed in a known quantity of water. The fuel whose 
heating value is to be determined is represented by a 
small sample of known weight that is placed in the closed 
vessel. Oxygen gas in this vessel is usually at a pressure 
of twenty or more atmospheres, and the sample of fuel is 
burned explosively on ignition by an electric spark. The 
excess of oxygen present in the closed vessel makes com- 
plete combustion certain, and the entire amount of heat 
liberated is absorbed by the vessel itself and by the sur- 
rounding water. As the rise of temperature in the vessel 
and water are accurately noted, the heat units liberated by 
the combustion of the known weight of fuel are readily 
computed. This method of heat determination by the 
calorimeter is capable of great accuracy, and duplicate 
tests agree in their results to within less than one 
per cent. The heat yielded per unit weight of fuel on 
perfect combustion as determined from chemical analysis 
and by the calorimeter has been found to be the same in 
many cases to within less than i per cent. Most of the 
better known varieties of coal have been tested so often 
that their heatins^ values have become matters of 
record, and can be readily found when wanted. In order 
to indicate the range of variation and to show about what 
may be expected in heating value for the more common 
varieties of coal, the following figures have been selected 
from the results of a number of calorimeter tests reported 
by George H. Barrus, in Volume XIV. of the Transac- 
tions of the American Society of Mechanical Engineers: 



LIGHT, HEAT AND POWER. 89 

Anthracite coal, ii tests; percentage of ash, 9.1 to 10.5; 
total heat of combustion, 11,521 to 13,189 heat units per 
pound. 

SEMI-BITUMINOUS COAL. 

George's Creek, Cumberland, Md., 10 tests; ash, 6.1 to 
8.6 per cent.; total heat of combustion, 12,874 to I4»2I7 
heat units per pound. 

Pocahontas, Va., 5 tests; ash, 3.2 to 6.2 per cent.; total 
heat of combustion, 13,608 to 13,922 heat units per pound. 

New River, Va., 6 tests; ash, 3.5 to 5.7 per cent.; total 
heat of combustion, 13,858 to 13,922 heat units per pound. 

Welsh, I test; ash, y.y per cent.; total heat of combus- 
tion, i2,iS2 heat units per pound. 

BITUMINOUS COAL. 

Yohoghany, Pa., lump ash, 5.9 per cent. ; total heat 
of combustion, 12,941 heat units per pound. 

Frontenac, Kansas, ash, 17.7 per cent. ; total heat of 
combustion, 10,506 heat units per pound. 

Cape Breton (Caledonia), ash, 8.7 per cent.; total heat 
of combustion, 12,420 heat units per pound of coal. 

Lancashire, England, ash, 6.8 per cent. ; total heat of 
combustion, 12,182 heat units per pound of coal. 

With boilers and furnaces of perfect efificiency, the 
combustion of coal would be complete, and all of the gen- 
erated heat would be transferred to the contained water 
and steam. It is interesting to note the evaporation of 
water per pound of coal that would be possible under sucK 
perfect conditions. Take first the case of the anthracite 
coal given above, having a heating power of 13,189 heat 
units per pound. As 966 heat units are necessary to 
change one pound of water at a temperature of 212 de- 
grees to steam at atmospheric pressure, the total heat of 
com.bustion for one pound of this anthracite coal is sufTi- 



CO LIGHT, HEAT AND POWER. 

cient to evaporate 13,189 -f- 966 = 13.6 pounds of water 
from and at 212 degrees. 

With a furnace and boiler of 80 per cent, efficiency, 
about the highest figure attainable in practice, the anthra- 
cite coal just mentioned will evaporate 13.6 x .80 = 10.88 
pounds of water from and at 212 degrees per pound of 
the coal burned. 

Taking the best result with semi-bituminous coal — that 
is, 14,217 heat units per pound — it appears that 14,217 -^ 
966 = 14.7 pounds of water may be evaporated from and 
at 212 degrees by its total heating value per pound. A 
boiler and furnace of 80 per cent, efficiency with this coal 
would be able to evaporate 14.7 x .80 = 11.76 pounds of 
water from and at 212 degrees per pound of the coal 
consumed. 

The bituminous coals nam'ed in this test have lower 
heating powers than those used in the computations just 
made, so that the possible evaporation with any of them 
would obviouslv be smaller. 

An essential difference between anthracite, semi-bitu- 
minous and bituminous coals is found in the percentage of 
fixed carbon and volatile matter in each of these varieties. 
Anthracite coal contains a larger per cent, of fixed carbon 
and a smaller per cent, of volatile matter than any of the 
other varieties. In Volume XIV. of the Transactions of 
American Institute of Mechanical Engineers, a re- 
port is given of the analysis of over thirty samples of 
anthracite coal, each taken from lots of 100 to 200 tons, 
as sent to market. These samples were all from the coal 
fields of Pennsylvania, being divided between the North- 
ern field, near Wilkesbarre; the Eastern Middle, or Le- 
high; the Western Middle, near Shenandoah, and the 
Southern field, from Mauch Chunk to Tamaqua. The 



LIGHT, HEAT AND POWER. 



91 



following table gives the results of some of these analyses 
for coals of all sizes mixed together: 



O^ t. 



p 0) J *^ r; ii 5 



CO ?0 (M CO (M !M O 

(^^'^^oa(^^!^^(^^(^^(^^^^l5^r-lr^ 
J? c^i^S 



<» 
to 
a 
■«-> 
a 

O 
t-> 






•< CO lO o 



MlOopODOOCCOO© 



O CO 00 Ol tH (N 
■^* 05 r-i OO 00 



— flOoocJS'^QCcDr-THi^ 
^OTT^cOirtitHOJCOaOXiN 



_►< fH w> CD 



„_ _ .. .-(t-c^Oeoco 

r,-eijXa0O030O0GOQOXQO 



r^i^QOQOlNMCOlOOOGCCiO 
crftJOOb-t-iH050i(MC0 

oScocococo-^cocorjH-^ 



^tHC^JtWCO'^^tHosC^ 

^oo'^tHcocococococoM 



'6 <v o ^ ^ ^ 

"q; S S 2 S S 

«ci 'o -S 2 !2 !2 

"S i i ^ ^ ^ 






(1) <P 



§ 1 ^ .^ 11 I § 1 o 



JO 



p hi 



_ 3 



O 



O 

P -C3 ^ 



o o 

^ ^ -^aSa 

a_^aas'ga^aa 



92 LIGHT, HEAT AND POWER. 

As the size of coal grows smaller, the relative amount 

of contained ash increases. Analyses of several sizes from 

one mine covered by the above tests gave the results of 

the following table: 

r- — Analyses. — -^ 

r- Screened. ^-^ Fixed 

Size. Through. Over. carbon. Ash. 

Egg coal 2.5 ins. 1.75 ins. 8S.49 5.66 

Stove coal 1.75 " 1.25" 83.67 10.17 

Chestnut coal 1.25 " .75 " 80.72 12.67 

Pea coal 75 " .50" 79.05 14.66 

Buckwheat coal 50 " .25" 76.92 16.62 

These figures plainly show that the fuel value of coal 
from any given mine decreases with the size of the lumps, 
since the per cent, of fixed carbon is less and the per cent, 
of ash greater in the smaller coals. 

What are known as the semi-anthracite, semi-bitumin- 
ous and the bituminous coals. differ from anthracite mainly 
as to the relative amounts of volatile matter and fixed car- 
bon in each. Just where the Hues should be drawn to 
separate the several varieties is a matter of some differ- 
ence of opinion, but it is not of great importance as long 
as the composition of the coal used in any particular case 
is known. 

The sixth volume of the Transactions A. I. M. E., page 
430, contains the results of test by Rogers on anthracite, 
semi-anthracite and semi-bituminous coals, as follows: 
Sixteen analyses of hard, dry anthracites give fixed car- 
bon a range of 82.47 to 94.10 per cent.; volatile matter, 
1.40 to 9.53 per cent., and 4.50 to 8.00 per cent, of ash, 
water and impurities. The ratio of these tests for carbon 
to volatile matter thus rano-e from 8.64 to 67.02. For 
semi-anthracite coal twelve tests gave a range of 74.55 to 
90.23 per cent, for fixed carbon, 7.07 to 13.75 per cent, for 
volatile matter, and for water, impurities and ash, 2.20 to 
12.10 per cent. Here the ratio of fixed carbon to volatile 



LIGHT, HEAT AND POWER. 93 

matter is 5.41 to 12.75. With ten analyses of semi-bitu- 
minous coals the per cent, of fixed carbon ranged from 
68.41 to 84.80, of volatile matter 11.2 to 17.28, and for 
impurities, water and ash 4 to 13.99. 

In this last case the ratio of fixed carbon to volatile 
matter goes from 3.96 to 11. 41. Following are given the 
results of several analyses selected from about fifty in the 
reports of the Pennsylvania Geological Survey. The 
figures here given all relate to bituminous coals, as may 
be seen from the low ratio of fixed carbon to volatile mat- 
ter: Green county coal, five analyses, fixed carbon, 59.72 
per cent. ; volatile matter, 40.28 per cent. ; ratio carbon to 
volatile matter, 1.48. Washington county coal, five an- 
alyses, fixed carbon, 53.22 per cent.; volatile matter, 46.78 
per cent.; carbon ratio to volatile matter, 1.13. Lower 
Bench, Washington county coal, five analyses, fixed car- 
bon, 50.97 per cent.; volatile matter, 49.03 per cent.; ratio 
of fixed carbon to volatile matter, 1.04. Jefferson county, 
Ohio coal, fixed carbon, 61.45 per cent. ; volatile matter, 
38.55 per cent.; ratio fixed carbon to volatile matter, 1.59. 

The figures given from the report last named take no 
account of the water, ash and impurities in the coal tested, 
but have been reduced so as to include the combustible 
portion only. The differences as to contained fixed car- 
bon and volatile matter in coals are of particular import- 
ance because of the marked effect on practical heating 
results, due to variations in the proportions of these ele- 
ments. With ordinary boilers and furnaces the practical 
heating value of bituminous coal is much lower than its 
actual heating value on perfect combustion. This differ- 
ence is due to the fact that boilers and furnaces, unless 
especially fitted for the use of bituminous coal, have a de- 
cidedly lower efficiency with it than they show when hard 



94 LIGHT, HEAT AND POWER. 

anthracite coal is employed. The volatile portion of the 
bituminous coal is rapidly distilled as gas after the coal is 
put into a furnace, and this gas is very apt to escape to the 
chimney unburned. With anthracite coal containing as 
much as 96 per cent, of the combustible portion in the 
form of fixed carbon, the boiler efficiency may be as high 
as 80 per cent. In the best of the grades of coal that have 
not more than 80 per cent, of fixed carbon, such as Cum- 
berland, it is hard to obtain an efficiency of more than 75 
per cent. Where the fixed carbon in coal is as low as 60 
per cent., a boiler efficiency of 65 per cent, is seldom ex- 
ceeded. In the use of coals having little more than 50 per 
cent, of fixed carbon, the boiler efficiency is most often 
below 60 per cent. 

The rapid falling off in efficiency with an increase in the 
volatile portion of coals is due not only to the escape of 
the gases distilled from the coal before they have been 
burned, but also to the thick deposits of soot that form 
rapidly on many parts of the boiler heating surfaces where 
these coals are used. 

With coals that contain less than 20 per cent, of volatile 
matter almost any of the ordinary types of boiler furnaces 
will give good results if properly proportioned and fired. 
Where 20 to 40 per cent, of volatile matter is present in 
the coal, a good form of furnace includes plain grate 
bars and a rather low arch of firebrick over them, so as to 
keep the temperature of the combustion chamber at a 
point sufficiently high to ignite the gases distilled from the 
coal. If the coal contains more than 40 per cent, of vola- 
tile matter, the furnace should have a large combustion 
chamber surrounded by firebrick to maintain the highest 
possible temperature. 

In connection with this last mentioned furnace, the air 



LIGHT, HEAT AND POWER. »5 

necessary for combustion should be raised to a high tem- 
perature before it is introduced to the furnace. The best 
equipment for the use of coal high in volatile matter in- 
cludes a gas producer, so that the coal gases as well as the 
air may be brought to a high temperature before their 
admission to the combustion chamber. The ordinary 
kind of boiler furnace, where the boiler surfaces are 
directly above the grate bars and receive the radiant heat 
of the fire, is especially to be avoided with coals that con- 
tain 20 per cent, or more of volatile matter, because the 
combustion chamber thus formed is sure to have a rather 
low temperature. A down draft that forces the distilled 
gases through the bed of coal on the grate, also the feed- 
ing of new coal underneath that already on the grate, has 
been found to increase efficiency where volatile matter is 
present in large amounts. 

While coal is the most important single fuel, there are 
others that find extensive use in some parts of the coun- 
try. At particular points certain fuels, such as wood, nat- 
ural gas and petroleum, may be cheaper than coal for a 
given heating effect, and are there naturally used on the 
score of economy. In many large cities there are serious 
and growing objections to the extensive use of coal. For 
anthracite coal the most important objection to its use in 
large buildings and manufacturing plants is that of cost, 
which is frequently 50 to 100 per cent, greater than that of 
bituminous coal of equal heating capacity. Bituminous 
coal, though cheap in price, meets with serious objection 
for city use because of the smoke resulting from its com- 
bustion, so that it is prohibited in some places. Another 
important hindrance to the use of bituminous coal is 
found in the fact that efficient combustion with it can only 
be had in certain special forms of furnace. A further dis- 



96 LIGHT, HEAT AND POWER. 

advantage that applies to both sorts of coal for most large 
city plants is found in the expense of hauling coal and in 
the removal of ashes by teams. Some of the undesirable 
features of coal are avoided by other kinds of fuel to a 
greater or less extent. 

COKE. 

Considered as to first cost, general desirability and the 
extent of its use, coke ranks next to coal in fuel impor- 
tance. Coke is made from bituminous coal, either by par- 
tial combustion in ovens or by distillation in retorts. The 
oven coke is generally more desirable for fuel purposes 
than that made in retorts at gas works. Dry coke varies in 
composition with the coal from which it is made, as to the 
proportions of its ingredients, but average figures may be 
taken as 90 per cent, carbon, 9 per cent, ash and i per 
cent, sulphur. It may be noted from this that the com- 
position of good coke differs but httle from that of the best 
p-rades of anthracite coal. In the process of coke making 
the volatile portions of the bituminous coal used are 
driven ofif as gas or consumed. The reduction in weight 
from the coal to the coke by this process is 30 to 40 per 
cent., leaving 60 to 70 per cent, of the weight of the coal 
used as coke. The fuel value of coke depends on its con- 
tained carbon, and taking this at 90 per cent, of the total 
weight, one pound of coke on perfect combustion de- 
velops 14,500 X .9 = 13,050 heat units, since the heating 
power of one pound of pure carbon is 14,500 heat units. 
As the fuel value of coke is thus about the same as that of 
anthracite coal, and as its price is usually between the 
prices of bituminous and anthracite, it forms a desirable 
substitute for these coals in some cases on the score of 
either greater economy or more desirable qualities. Un- 
Hke bituminous coal, coke requires no special form of fur- 



LIGHT, HEAT AND POWER. OJ 

nace for its satisfactory combustion, and is as free from 
smoke as the best anthracite coal. At present gas retorts 
furnish most of the coke available in cities for general use, 
but there seems to be a movement toward the substitution 
of ovens for retorts in gas making. 

ILLUMINATING GAS. 

Another product from coal that may serve as fuel iii 
some cases is illuminating gas, but it is only available in 
special cases or where the item of cost is of minor impor- 
tance. The value of illuminating gas as a fuel is approxi- 
mately 650 heat units per cubic foot on perfect combus- 
tion, so that 1,000 cubic feet of gas yields 650,000 heat 
units. As one dollar is about the lowest current price for 
illuminating gas per 1,000 feet, the 650,000 heat units may 
be taken as the heat available from gas for that sum. It 
anthracite coal costs five dollars per ton, 400 pounds may 
be obtained for one dollar, and allowing 13,000 heat units 
per pound for this coal, the total heating value is 13,000 x 
400 = 5,200,000 units. Under these conditions, there- 
fore, the gas is 5,200,000 -^ 650,000 = 8 times as expen- 
sive as anthracite coal. 

NATURAL GAS. 

In some parts of the country where natural gas is 
abundant it may and does displace coal as fuel to soni^ 
extent. The heating power of natural gas is much greater 
than that of coal gas, and may be fairly taken at 1,000 
heat units per cubic foot on an average, so that 1,000 cubic 
feet yield 1,000,000 units of heat. Comparing natural gas 
with anthracite coal at five dollars per ton, in which one 
dollar purchases a heating power of 5,200,000 units, it 
appears that 5,200,000 -^ 1,000,000 =5.2 times 1,000 
cubic feet of natural gas must be supplied to obtain as 



98 LIGHT, HEAT AND POWER. 

much heat as may be had from coal costing one dollar. 
Natural gas must therefore sell for loo -7- 5.2 = 19.2 cents 
per 1,000 cubic feet to be equally cheap with anthracite 
coal for fuel. The absence of smoke and ashes, also the 
saving of labor, where natural gas is available raise the 
price at which it really competes with coal somewhat 
above the figure just found. 

WOOD AS FUEL. 

Wood continues to be an important fuel for even large 
establishments in many parts of the United States. Dif- 
ferent varieties of wood vary widely as to their heating 
powers, so that the number of cubic feet or cords 
alone is no definite indication of the heat that may 
be obtained from it. The heating power of wood 
varies in very nearly the same proportion as its weight 
when it is perfectly dry. Average weights for perfectly 
dry wood are: White pine, 25 pounds; white oak, 48 
pounds; maple, 50 pounds; red oak 40 pounds per cubic 
foot. One cord of wood occupies a space of 128 cubic 
feet, but a greater or less portion of this space is actually 
filled by the wood, according to the size and straightness 
of the sticks. An average figure for the number of cubic 
feet of solid wood in one cord is 60. On this basis a cord 
of maple, perfectly dry, weighs 50 x 60 = 3,000 pounds. 
Perfectly dry wood is only obtained by some artificial 
process of drying, and air dried wood contains 20 to 25 
per cent, of water at best. It follows that a cord of maple 
wood, as dry as it can be got in the open air, weighs about 
4,000 pounds. Perfectly dry wood of most varieties is 
nearly uniform in chemical composition, except that some 
pine wood has more than the usual proportion of hydro- 
gen. Average figures for the composition of wood are: 



LIGHT. HEAT AND POWER. 99 

Carbon, 50; oxygen, 42; hydrogen, 6; nitrogen, i, and 
ash, I per cent. The nitrogen and ash have no fuel value, 
and if the figures for the other elements are substituted 
in Dulong's formula, the result is (14,500) .5 + 62,000 

.42 

(.06 ) = 7,715 heat units. In the case of air-dried 

8 

wood having 20 per cent, of water, the heat units per 
pound are reduced to 7,715 x .8 = 5,929. Even this 
amount of heat cannot be realized for any useful pur- 
pose, because the water in the wood must be evaporated 
on combustion. It may be assumed that 150 heat units 
are necessary to raise the temperature of one pound of 
water in the wood from that of the air to 212 degrees. 
To evaporate one pound of water at 212 degrees requires 
966 heat units, and about 100 more units of heat are neces- 
sary to bring the temperature of one pound of steam up to 
that of the fire, making a total of 1,216 heat units per 
pound of water in the wood. If each pound of air-dried 
wood contains 20 per cent, of water, 1,216 x .2 = 243.2 
heat units must be expended in its water when the wood 
is burned, leaving 5,929 — 243 = 5,686 heat units pef 
pound of maple wood for useful purposes. 

Allowing anthracite coal a heating power of 13,000 
units per pound, it appears that one pound of maple wood 
will develop 5,686 -^ 13,000 = 43 per cent, of the heat 
that may be had from a pound of this coal. As one cord 
of this wood weighs 4,000 pounds, or two tons, the wood 
is equivalent to .43 x 2 = 86 per cent, of a ton of the coal 
in heating power. If the ton of coal costs five dollars, tht 
maple wood will be equally cheap as fuel when it costs $5 
X .86 = 4.30 dollars per cord. Hickory has fully as much 
heating power per cord as maple, white oak has a little 



100 LIGHT, HEAT AND POWER. 

less, and white pine only one-half. Wet and green wood 
may weigh as much as 50 per cent, more than that which 
is perfectly dry, but the additional water causes a material 
loss in the available heating power in a given bulk of the 
wood, because this water must be evaporated when the 
wood is burned. A furnace for wood should be larger 
than one for coal to obtain a given heating effect, because 
of the greater bulk of the former, but no other special 
features are necessary. With good draft wood bums 
without much smoke, and the volume of ash is relatively 
small, so that it is a desirable fuel in these respects. 

CHARCOAL. 

Charcoal holds something the same relation to wood 
that coke does to coal; that is, charcoal is the residue, 
mainly of carbon, left by the partial combustion of wood 
under conditions where the air is in large part excluded, 
or by heating wood in closed retorts. With air-dried 
wood heated to produce charcoal, the weight of the prod- 
uct is two to three-tenths of that of the wood consumed, 
according to the process employed. Charcoal, as it comes 
from the furnace, is almost perfectly dry, but it absorbs 
water rapidly from the air, and its proportion of moisture 
rises to as much as 10 per cent, after a few days. The 
compositon of charcoal ordinarily sold may be taken at 
85 per cent, carbon, 10 per cent, water, 4 per cent, ash and 
I per cent, hydrogen. As the heating power of carbon is 
14,500 units per pound, one pound of ordinary charcoal 
may be expected to yield 14,500 x .85 = 12,7,2^ heat units 
on combustion, or 95 per cent, of the heat from one pound 
of good anthracite coal. It follows that about 2,100 
pounds of charcoal will furnish as much heat as one ton 
of anthracite coal. Charcoal is commonly sold by the 



LIGHT, HEAT AND POWER. 101 

bushel, and the weight of this volume is about 15 to 30 
pounds, according to the kind of wood from which the 
charcoal is made. For oak and maple charcoal the weight 
is about 30 pounds per bushel, so that 2,100 -f- 30 = 70 
bushels are required to equal in heating capacity one ton 
of good anthracite coal. Because of its small per cent, of 
ash and freedom from smoke when burning, charcoal is a 
very desirable fuel, but its price is such that it cannot com- 
pete with coal for general use, except in a few localities. 
Charcoal has, however, an extensive application for special 
heating purposes, and competes with gas as a fuel for 
cooking in hot weather. Peat, as well as wood, can be 
used in the production of charcoal, but wood is much 
more generally employed for the purpose in the United 
States. 

PEAT. 

Peat is extensively used for fuel in some parts of Eu- 
rope, but has as yet been little applied in the United States. 
Large deposits of peat are known to exist here, however, 
and a moderate increase in the average price of coal would 
probably give them importance as fuel. Peat, after being 
removed from its natural beds and air-dried, contains 
about 25 per cent, of water. Perfectly dry peat contains 
in 100 parts by weight about 58 parts of carbon, 6 parts 
of hydrogen, 30 parts of oxygen and 6 parts of ash. Ap- 
plying Dulong's formula to this composition, gives the 
heating power of one pound of perfectly dry peat as .58 

•30 

(14,500) + 62,000 (.06 ) = 9,805 heat units. Where 

8 

the peat is air-dried and contains 25 per cent, of moisture, 
the heating power per pound drops to 9,805 x .75 = 7,353 
heat units. To evaporate one pound of water from the 



102 LIGHT, HEAT AND POWER. 

peat will require, as in the case of wood, about 1,216 heat 
units, so that the one-fourth pound of water in one pound 
of air-dried peat absorbs 1,216 -^ 4 = 304 heat units on 
combustion. The net available heat per pound of peat is 
thus 7,353 — 304 = 7,049 heat units, or about 7,049 -r- 
1,300 = 54 per cent, of that for anthracite coal. 

PETROLEUM. 

Petroleum is sufficiently abundant to be used as fuel to 
some extent, and it is very desirable for this purpose, as to 
the absence of smoke and ashes. The approximate chem- 
ical composition of 100 parts of petroleum is 85 parts car- 
bon, 13 parts hydrogen and 2 parts oxygen. These 
values substituted in Dulong's formula give the heating 
power of one pound of crude petroleum as .85 (14,500 + 

,02 

62,000 (.13 ) = 20,230 heat units. Petroleum is 

8 

usually quoted by the gallon, of which the average weight 
is about ^.y pounds. The heating power per gallon is 
therefore 20,230 x d.y = 135,541 heat units, so that the 
gallons to equal one ton of anthracite coal in heating 
I power are found from (13,000 x 2,000) -^ 135,541 = 192. 

To equal anthracite coal in cost per unit of heating power, 
when the coal is worth five dollars per ton, the petroleum 
may therefore cost 500 -i- 192 = 2.6 cents, per gallon. 
Compared with coal, petroleum offers some saving in the 
cost of firing, but in spite of this and its other desirable 
features, its price is usually such as to prohibit its use for 
fuel, aside from some special cases. 



CATALOGUE 



OP 



Architectural and Scientific Books 

BDILDING CONSTBDCTION 

AND SgPEBIIITEIIDENCE. 

By F. E. EIDDEE, C. E., PL D. Architect. 

Author of " The Architects' and Builders' Pocket Book." 



Part I.— MASONS' WORK. 

(4th Edition) 
4SZ Pages, 250 Illustrations, 



Part II.— CARPENTERS* WORK. 

(3rd Edition) 
S44 Pages, 524 Illustrations, 



It has been the aim of the Author, in preparimg 
these works, to furnish a series of books that shall be 
of practical value to all who have to do with building 
operations, and especially to architects, draughtsmen 
and builders. 

Each volume is independent and they are sold 
separately. 

Th£ volumes are large 8vos. bound in cloth, 
price $4.00 each. 



FULL DESCRIPTIVE CIRCULAR SENT ON APPUCATIOK. 

William T. Comstock, 23 Warren St., New York. 



104 CATALOGUE OF 



Sanitary Engineering of Buildings. 



•\7"ol. I- 



By WM. PAUL GERHARD, C. E., 

Consulting Engineer for Sanitary Works, 

Mem. Am, Public Health Association, Cor. Mem. American 
Institute of Architects. 

Each Volume independent and sold separately. 
One large 8vo Vol. 454 pages. 103 Ills. & 6 Plates. 

t&~Sample Page on application. 

SECOND EDITION 

SPECIFICATIONS. 

A PRACTICAL SYSTEM FOR WRITING 
SPECIFICATIONS FOR BUILDINGS S ^ 

By W. FRANK BOWER. 

This is the first and only work ever published in which 
it has been attempted to make a complete compila- 
tion of specification matter covering, as nearly 
as could be done, every possible vari- 
ety of structural work. 

One volume, 240 pages, 9x12 inches, bound in dark green buck- 
ram, lettered in aluminum. 

PRICE. $5.00 



WILLIAM T. COMSTOCK, 



ARCHITECTURAL AND SCIENTIFIC BOOKS. 105 

JUST PUBI^ISH^D. 

NEW AND ENLARGED EDITION OF 

Churches and Chapels. 

62 P/ates and 120 //lustrations in the Text. 
By F. E. KIDDER, Architect. 

This book contains a large number of plans and perspectives of 
churches of varying costs. Beside? this there is much 
concise and practical information relating to 
planning and seating; cetails of Con- 
struction, Heating and Ventila- 
tion, Acoustics, etc. 

One oblong quarto volume, Cloth, - Price, $3.00 
2d American Edition of the Standard Work. 

VIGNOLA 

THE FIVE ORDERS OF fiRGHITEGTURE 

ACCORDING TO 

GIACOMO BAROZZI, OF VIGNOLA. 

TO WHICH ARE ADDED 
' yt-ti i^g Gr:FL:ES:EJOES. 0£1.33£S:FLJSy 

EDITED AND TRANSLATED BY 

ARTHUR LYMAN TUCKERMAN, 

FOR THE USE OF THE 

Art Schools of the Metropolitan Museum of Arts. 

The volume contains 84 plates with descriptive 
text in English, and will aflFord the student a ready 
reference to the details of the Greek and Roman orders. 
One Quarto Volume, CSoth, Price $5.00. 



23 WARREN STREET, NEW YORK. 



106 CATALOGUE OF 



laster Castsi?^ HowThey AreMade. 



With Full Illustrations. 

A plea for a more general appreciation of the artistic qualities 

and uses of Plaster of Paris Casts. A brief historical review 

of the art of casting from the time of the Greeks to the 

present. Directions for making casts by the waste, 

piece, elastic and sulphur mould processes. 

Casting from life, oiling, painting, cleaning, 

mending and packing casts, and 

notes upon clay modeling. 

By FRANK FORREST FREDERICK, 

Professor of Art and Design in the University of Illinois. 
Author of "Architectural Rendering in Sepia." 

One i6mo Volume, Cloth ; Price, $ 1..50 



AN INVALUABLE BOOK FOR ARCHITECT, 
STUDENT OR DRAUGHTSMAN j^S 

Architectural Rendering in Sepia. 

By FRANK FORREST FREDERICK, 

Professor of Industrial Art and Design, University of Illinois. 

Illustrated by Full Page Plates, reproduced 
from Water Colors by the Photogravure 
Process, together with descriptive text. 

This will be a valuable help to every Architect, Draughtsman 

and Architectural Student. By its ad rendering in Wash, 

Color and Sepia can be so learned as to enable the 

practitioner to put his perspectives readily in 

shape so he may show an attractive 

picture of his proposed house 

to his client. 

One Folio, Handsomely Bound in Cloth Price, 9!3.00 



WILLIAM T. COMSTOCK, 



ARCHITECTURAL AND SCIENTIFIC BOOKS. 107 



JUST PUBLISHED. 

Furniture Designing and Draughting. 

Notes on the Elementary Forms, Methods of 
Construction and Dimensions of Common 
Articles of Furniture 

This book is for the use of students, archi- 
tects and others who at times find it desirable 
to make drawings for furniture, has been pre- 
pared from material collected during an ex- 
perience of some years as a designer of furni- 
ture for several of the most important furniture 
makers in New York City. 

Octavo, Cloth, Price, $2.00. 



HAND RAILING SIMPLIFIED. 

Being an exposition of the Sectorian Sys- 
tem of developing ^and Railing. Edited 
and revised by Fred. T. Hodgson, Architect, 
member of O. A. A. 

This is the only book published which treats the art 
of Hand Railing throughout on the sectorian system, 
and the work seems to be done thoroughly. 

By this method any good workman who gives an hour 
or two to the study of the subject as exemplified in this 
little work, will be enabled to build a fair rail. 

45 Illustrations. One 16mo. volume. Cloth, Price, $1.00. 



23 WARREN STREET, NEW YORK. 



108 CATALOGUE OF 



FOURTH MDITION-RMVISMD. 



A Practical Book on Perspective. 

Architectural Perspective for Beginners. 
By F. A. WRIGHT, Architect 

Containing 11 large Pla ?s and full de- 
scriptive letter-press. One large quarto, 
handsomely bound in cloth 

Price, . . ... o . $3»oo 

PRACTICAL LESSONS in 
ARCHITECTURAL DRAWING 

Or, How to Make the Working Drawings for Buildings. Tenth 
Edition. Containing 44 pages of descriptive letterpress, 
illustrated by 33 fnll-page plates (one in colors) and 33 
wood cuts, showing methods of construction and 
representation. The work embraces scale draw- 
ings of plans, elevations, sections and details 
of frame, brick and stone building, with 
full descriptions and a form of speci- 
fications adapted to the same. 

Suited to the wants of architectural students, car- 
penters builders and all desirous of acquiring a 
thorough knowledge of architectural drawing and 
construction. ' •♦*— -3^5 

By William B. Tuthill, A. M., Architect. 
On£ large 8vo volume, oblong, cloth. Ptice, ^2*^0 



WILLIAM T. COMSTOCK, 



ARCHITECTURAL AND SCIENTIFIC BOOKS. 109 



JUST PUBLISHED 

Details of Building Construction, 

A collection of 33 plates of scale 
drawings, with introductory text 

Asst. Professor, College of Architecture, Cornell University. 

This book is lo x 12^ inches in size 
and substantially bound in cloth 

PRICE, $2.00 

Fouadations and Foaodatioo Walls. 

Pile Driving, Building Stones and Bricks. Treating of founda- 
tions, pier and wall constructions, mortars, limes, cements, 
concretes, stuccos, etc. Sixty-four illustrations. By the 
late Geo. T. Powkll, Architect and Civil Engineer, 
New York, to which is af'ded a treatise on 
foundations, with practical illustrations 
of the method of isolated piers 
as followed in Chicago. 
By Frederick Baumann, Architect. 

Fifth edition, new and enlarged. One 8vo volume, cloth. 

PRICE, $2.00 

Elementary Graphic Statistics and tbe Con- 
struction of Trussed Roofs. 

(Fourth Edition Revised.) 
BY Prof. N. C. RICKER. 

One 8vo volume, cloth. 158 pages, 115 illustrationi. 

PRICE. $2.00 



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110 CATALOGUE OF 



i Manual of Industrial Drawing for Car* 
penters and Other Woodworkers. 

By W. F. Dbckkr, Instructor of Drawing University of Minne* 

sota. Second edition revi%ed. 176 pages, 29 plates and numer- 

numerous other illustrations. One 8vo volume, cloth. 

Reduced from $2.00 to $j.50 

Hathematical Drawing Instruments and low 
to Use Tliem. 

One imperial i6mo volume, bound in cloth, containing 13a pages 

and 70 illustrations, including eleven different 

styles of lettering. 

PricCt • . . $T,5o 

Draughtsman's Manual ; or, How Can I Learn 
irchitecture ? 

By F. T. Camp. Containing hints to inquirers and directions 

in draughtsmanship. New, revised and enlarged edition. 

One small volume, cloth. 

Price, . . 50 Cents. 

PERSPECTIVE. 

By Ada Cone. A series of practical lessons beginning with ele- 
mentary principles and carrying the student through a 
thorough course in perspective. Thirty-three il- 
lustrations One i2mo volume, cloth. 

Price, . • $1.00 

Irchitectural Picture Making with Pen 
and Ink. 

" Old Erbor " Folios. By Bhnjamik Linfoot, Architect. With 
illustrations by the author. One large oblong quarto, cloth. 

Price, • • • • $3'5o 



WILLIAM T. COMSTOCK, 



ARCHITECTURAL AND SCIENTIFIC BOOKS. Ill 



Moflclrton's Practical Geometry. 

Being a series of lessons beginning with the simplest problems, 
and in the course embracing all of geometry likely to be re- 
quired for the use of every class of mechanics, or that 
are needed for instruction in mechanical schools. Il- 
lustrated by 42 full page plates By James H. 
MoNCKTON, author of "Moncton's National 
Carpenter and Joiner" and "Moncton's 
National Stair BuilHer." 
Instructor for many years in the Mechanics' aod Traders' Free 
Drawing School of the city of New York. 

One izmo volume, cloth. Price, prepaid, $1.00 

Atwood's Revised Rules of Proportion. 

Compiled and original and adapted to modern practice. 

By D. T. ATWOOD, Architect. 

Third edition, izmo, cloth. 

Price, 75 Cents, 

Bryan's Architectural Proportion. 

Ay A. J. BRYAN, Architect. 

A new system of proportion, showing the relation between an 
Order of Architecture and a Building of any kind. 

Illustrated. 
Price, , . $1.50 

Notes on Art of House Planning. 

By C. FRANCIS OSBORNE, Architect, 

Assistant Professor of Architecture in Cornell University. 

PricCt , • $z.oo 



23 WARREN STREET, NEW YORK. 



ARCHITECTS' 
AND BUILDERS' 
ii MAGAZINE ii 



ARCHITECTURE tTTT BUILDERS' 

AND BUILDING ^''°^°"''^*'"' MAGAZINE 

PUBLISHED MONTHLY 
DEVOVED TO THE INTERESTS OF 

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The illustrations are from line and halftone plates, finely re- 
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It contains special technical and illustrated articles, scientific 
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In each number will be given a series of plates representing 
the latest current work, together with full descriptive letter-press, 
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other features of interest. 

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